Air Service Boys Over the Rhine; Or, Fighting Above the Clouds

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Air Service Boys Over The Rhine

Or, Fighting Above The Clouds

By Charles Amory Beach

AUTHOR OF "AIR SERVICE BOYS FLYING FOR FRANCE," "AIR SERVICE BOYS OVER THE ENEMY'S LINES," ETC.

Illustrated By Robert Gaston Herbert

The Saalfield Publishing Co. Akron, Ohio New York

Made In U.S.A.

Copyright, 1919, By George Sully & Company

[Illustration: BLOWING UP THE GERMAN MUNITION FACTORY.]

Contents

I Double News

II Anxious Days

III On To Paris

IV Suspicions

V The Bombardment Of Paris

VI The Rue Lafayette Ruins

VII Tom'S Father

VIII Where Is Mr. Raymond?

IX Various Theories

X The "Dud"

XI A Monster Cannon

XII For Perilous Service

XIII The Spy

XIV With Comrades Again

XV The Picked Squadron

XVI Missing

XVII Seeking The Gun

XVIII A Cloud Battle

XIX Queer Lights

XX The Big Gun

XXI Devastating Fire

XXII Over The Rhine

XXIII Off For Germany

XXIV Prisoners

XXV The Escape

Air Service Boys Over The Rhine

Chapter I

Double News

"Here they come back, Tom!"

"Yes, I see them coming. Can you count them yet? Don't tell me any of our boys are missing!" and the speaker, one of two young men, wearing the uniform of the Lafayette Escadrille, who were standing near the hangars of the aviation field "somewhere in France," gazed earnestly up toward the blue sky that was dotted with fleecy, white clouds.

There were other dots also, dots which meant much to the trained eyes of Tom Raymond and Jack Parmly, for the dots increased in size, like oncoming birds. But they were not birds. Or rather, they were human birds.

The specks in the sky were Caudrons. A small aerial fleet was returning from a night raid over the German ammunition dumps and troop centers, and the anxiety of the watching young men was as to whether or not all the airmen, among whom were numbered some of Uncle Sam's boys, had returned in safety. Too many times they did not--that is not all--for the Hun anti-aircraft guns found their marks with deadly precision at times.

The Caudrons appeared larger as they neared the landing field, and Tom and Jack, raising their binoculars, scanned the ranks--for all the world like a flock of wild geese--to see if they could determine who of their friends, if any, were missing.

"How do you make it, Tom?" asked Jack, after an anxious pause.

"I'm not sure, but I can count only eight."

"That's what I make it. And ten of 'em went out last night, didn't they?"

"So I heard. And if only eight come back it means that at least four of our airmen have either been killed or captured."

"One fate is almost as bad as the other, where you have to be captured by the Boches," murmured Jack. "They're just what their name indicates--beasts!"

"You said something!" came heartily from Tom. "And yet, to the credit of airmen in general, let it be said that the German aviators treat their fellow, prisoners better than the Hun infantrymen do."

"So I've heard. Well, here's hoping neither of us, nor any more of our friends, falls over the German lines. But look, Tom!" and Jack pointed excitedly. "Are my eyes seeing things, or is that another Caudron looming up there, the last in the line? Take a look and tell me. I don't want to hope too much, yet maybe we have lost only one, and not two."

Tom changed the focus of his powerful glasses slightly and peered in the direction indicated by his chum. Then he remarked, with the binoculars still at his eyes:

"Yes, that's another of our machines! But she's coming in slowly. Must have been hit a couple of times."

"She's lucky, then, to get back at all. But let's go over and hear what the news is. I hope they blew up a lot of the Huns last night."

"Same here!"

The aircraft were near enough now for the throbbing of their big motors to be heard, and Tom and Jack, each an officer now because of gallant work, hurried across the landing field.

It was early morning, and they had come, after a night's rest, to report for duty with others of the brave Americans who, during the neutrality of this country in the great conflict, went to France as individuals, some to serve as ambulance drivers, others to become aviators.

The Caudron is the name given to one type of heavy French aeroplane carrying two or more persons and tons of explosive bombs.

An air raid on the German lines by a fleet of these machines had been planned. It had been timed for an early hour of the night, but a mist coming up just as the squadron of heavy machines, each with two men and a ton or more of explosives, was ready to set out, the hour had been changed. So it was not until after midnight that the start had been made.

And now the boys were coming back--that is all who were able to return. One machine was missing. At least, that was the assumption of Tom and Jack, for they could count but nine where there should have been ten. And of the nine one was coming back so slowly as to indicate trouble.

One by one the machines, which ordinarily came back before daybreak, landed, and the pilot and the observer of each climbed clumsily down from their cramped seats. They were stiff with cold, in spite of the fur-lined garments they wore--garments that turned them, for the moment, into animated Teddy bears, or the likeness of Eskimos.

Their faces were worn and haggard, for the strain of an airship bombing raid is terrific. But they were quiet and self-possessed as they walked stiffly across the field to make a report.

"Any luck?" asked Tom, of one he knew; a Frenchman noted for his skill and daring.

"The best, _mon ami_," he replied with a smile--a weary smile. "We gave Fritz a dose of bitter medicine last night."

"And he gave us a little in return," sadly added his companion. "Quarre and Blas--" he shrugged his shoulders, and Tom and Jack knew what it meant.

They were the men in the missing machine, the Caudron that had not come back.

"Did you see what happened?" asked Jack.

Picard, to whom Tom had first spoken, answered briefly.

"They caught them full in the glare of a searchlight and let them have it. We saw them fall. There didn't seem to be any hope."

"But the battery that did the firing--it is no more," added De Porry, the companion of Picard. "The bombs that Quarre and Blas carried went down like lead, right on top of the Hun guns. They are no more, those guns and those who served."

"It was a retributive vengeance," murmured Picard.

Then they passed on, and others, landing, also went to make their reports.

Some of them had reached their objectives, and had dropped the bombs on the German positions in spite of the withering fire poured upward at them. Others had failed. There is always a certain percentage of failures in a night bombing raid. And some were unable to say with certainty what damage they had caused.

The last slowly flying machine came to a landing finally, and there was a rush on the part of the other aviators to see what had happened. When Tom and Jack saw a limp form being lifted out, and heard murmurs of admiration for the pilot who had brought his machine back with a crippled engine, they realized what had happened.

The two brave men had fulfilled their mission; they had released their bombs over an important German factory, and had the terrible satisfaction of seeing it go up in flames. But on their return they had been caught in a cross fire, and the observer, who was making his first trip of this kind, had been instantly killed.

The engine had been damaged, and the pilot slightly wounded, but he had stuck to his controls and had brought the machine back.

There was a little cheer for him, and a silent prayer for his brave companion, and then the night men, having made their reports, and having divested themselves of their fur garments, went to rest.

"Well, what's on the programme for to-day, Tom?" asked Jack, as they turned back toward the hangars where they had their headquarters with others of their companions in the Lafayette Escadrille and with some of the French birdmen.

"I don't know what they have on for us. We'll have to wait until the orders come in. I was wondering if we would have time to go and see if there's any mail for us."

"I think so. Let's go ask the captain."

They had, of course, reported officially when they came on duty, and now they went again to their commanding officer, to ask if they might go a short distance to the rear, where an improvised post-office had been set up for the flying men.

"Certainly, messieurs," replied the French captain, when Tom proffered the request for himself and his chum. "Go, by all means." He spoke in French, a good mastery of which had been acquired by our heroes since their advent into the great war. "Your orders have not yet arrived, but hold yourselves in readiness. Fritz is doubtless smarting under the dose we gave him last night, and he may retaliate. There is a rumor that we may go after some of his sausages, and I may need you for that."

"Does he mean our rations have gone short, and that we'll have to go collecting bolognas?" innocently asked a young American, who had lately joined.

"No," laughed Tom. "We call the German observation balloons 'sausages.' And sometimes, when they send up too many of them, to get observations and spoil our plans for an offensive, we raid them. It's difficult work, for we have to take them unawares or they'll haul them down. We generally go in a double squadron for this work. The heavy Caudrons screen the movements of the little Nieuports, and these latter, each with a single man in it, fire phosphorus bullets at the gas bags of the German sausages.

"These phosphorus bullets get red hot from the friction of the air, and set the gas envelope aglow. That starts the hydrogen gas to going and--good-night to Mr. Fritz unless he can drop in his parachute. A raid on the sausages is full of excitement, but it means a lot of preparation, for if there has any rain or dew fallen in the night the gas bags will be so damp that they can't be set on fire, and the raid is off."

"Say, you know a lot about this business, don't you?" asked the young fellow who had put the question.

"Nobody knows a _lot_ about it," replied Jack. "Just as soon as he does he gets killed, or something happens to him. We're just learning--that's all."

"Well, I wish I knew as much," observed the other enviously.

Tom and Jack walked on toward the post-office, being in rather a hurry to see if there was any mail for them, and to get back to their stations in case their services were needed.

As they went along they were greeted by friends, of whom they had many, for they had made names for themselves, young as they were. And, as a matter of fact, nearly all the aviators are young. It takes young nerves for the work.

"Here's one letter, anyhow!" observed Tom, as he tore open a missive that was handed to him. "It's from dad, too! I hope he's all right. He must have been when he wrote this, for it's in his own hand."

"I've got one from my mother," said Jack. "They're all well," he went on, quickly scanning the epistle. "But they haven't received our last letters."

"That isn't surprising," said Tom. "The mail service is fierce. But I suppose it can't be helped. We're lucky to get these. And say!" he exclaimed excitedly, as he read on in his letter. "Here's news all right--great news!"

Jack looked at his chum. Tom's face was flushed. The news seemed to be pleasurable.

Jack was about to ask what it was, when he saw a messenger running from the telephone office. This was the main office, or, at least, one of the main offices, in that section, and official, as well as general, news was sometimes sent over the wire.

The man was waving a slip of paper over his head, and he was calling out something in French.

"What's he saying?" asked Jack.

"Something about good news," answered Tom. "I didn't get it all. Let's go over and find out. It's good news all right," he went on. "See! they're cheering."

"More news," murmured Jack. "And you have some, too?"

"I should say so! Things surely are happening this morning! Come on!" and Tom set off on a run.

Chapter II

Anxious Days

While Tom and Jack were hastening toward the man who seemed to have received some message, telephone, telegraph or wireless, from the headquarters of this particular aviation section, a throng of the aviators, their mechanicians, and various helpers, had surrounded the messenger and were eagerly listening to what he had to say.

"I wonder what it can be, Tom," murmured Jack, as the two fairly ran over the field.

Those of you who have read the two preceding volumes of this series will remember Tom Raymond and Jack Parmly. As related in the first book, "Air Service Boys Flying for France; or The Young Heroes of the Lafayette Escadrille," the youths had, some time previously, gone to a United States aviation school in Virginia, their native state, and there had learned the rudiments of managing various craft of the air. Tom's father was an inventor of note, and had perfected a stabilizer for an aeroplane that was considered very valuable, so much so that a German spy stole one of the documents relating to the patent.

It was Tom's effort to get possession of this paper that led him and, incidentally, his chum Jack into many adventures. From their homes in Bridgeton, Virginia, they eventually reached France and were admitted into that world-famed company--the Lafayette Escadrille. Putting themselves under the tuition of the skilled French pilots, the Air Service boys forged rapidly to the front in their careers.

It was while on a flight one day that they attacked a man in a motor car, who seemed to be acting suspiciously along the sector to which our heroes were assigned, and they pursued him, believing him to be a German spy.

Their surmise proved correct, for the man, who was hurt when his machine got beyond control, was none other than Adolph Tuessig, the German who had vainly tried to buy Mr. Raymond's stabilizer from him, and who had, later, stolen the paper.

In our second volume, entitled, "Air Service Boys Over the Enemy's Lines; or The German Spy's Secret," Tom and Jack found further adventures. On their way to England, whence they had gone to France, they had met on the steamer a girl named Bessie Gleason. She was in the company of Carl Potzfeldt. The girl seemed much afraid of him, though he was her guardian, said to have been so named by Mrs. Gleason, a distant relative of his. Mrs. Gleason had been on the ill-fated _Lusitania_, and it was related by Potzfeldt, for purposes of his own, that Bessie's mother had been drowned. Moreover, he declared that before she died she had given him charge of Bessie.

Tom and Jack, the latter especially, grew very fond of Bessie, but there seemed to be a mystery about her and something strange in her fear of her guardian.

When the two young men reached England, they lost sight, for a time, of their fellow passengers, but they were destined to meet them again under strange circumstances.

During one of their flights they landed near a lonely house behind the German lines. They were traveling in a Caudron, which contained them both, and on investigating the building after dark they found, to their surprise, that Bessie and her mother were kept there, prisoners of Carl Potzfeldt, who was a German spy.

Bessie and her mother were rescued and then departed for Paris, the latter to engage in Red Cross work, and the boys, remaining with their fellow aviators, longed for the time when they might see their friends once more.

But they had enlisted to help make the world safe for democracy, and they intended to stay until the task was finished. Over a year had elapsed since the sensational rescue of Bessie and her mother. The United States had entered the war and the Air Service boys were thinking that soon they might be able to join an American aviation service in France.

"What is it? What has happened?" Tom demanded of one of the aviators on the outskirts of the throng about the messenger. "Have we won a victory over the Germans?"

"No, but we're going to," was the answer. "Oh, boy! It's great! We're in it now sure! Hurray!"

"In it? What do you mean?" asked Jack.

"I mean that Uncle Sam has at last stepped over the line! He's sure enough on the side of the Allies now, and no mistake."

"You mean--" cried Tom.

"I mean," answered Ralph Nelson, another American aviator, "that the United States has made a big success of the Liberty Bonds loan and is going to send a million soldiers over here as soon as possible! Say, isn't that great?"

"Great? I should say so!" fairly yelled Tom. "Shake!" he cried, and he and his chum and everybody else shook hands with every one whose palm they could reach. And there were resounding claps on the back, and wild dances around the green grass, even the French joining in. No not that word "even," for the French, with their exuberance of spirit, really started the joy-making.

To the brave men, who, with the British, had so long endured the brunt of the terrible blows of the Huns alone, the efforts of the United States of America meant much, though it was realized that it would be some time before Uncle Sam could make his blows really tell, even though an Expeditionary Force was already in the field.

"Say, this is the best news ever!" said Jack to Tom, when quiet, in a measure, had been restored. "It's immense!"

"You said something, old man! It's almost as good news as if you had come in and told me that you had downed a whole squadron of German aircraft."

"I wish I could, Tom. But we'll do our share. Shouldn't wonder, before the day is out, but what we'd get orders to go up and see what we can spot. But I'm almost forgetting. You had some news of your own."

"Yes, I have. And now I have a chance to finish reading dad's letter."

"But first you can tell me what the special news is, can't you?" asked Jack. "That is, unless you think it will be too much for me to stand all in one day--your news and that about Uncle Sam's success in raising funds and troops."

"Oh, I guess you can stand it," said Tom with a smile. "It's this. Dad is coming over!"

"He is? To fight?"

"Well, no, not actively. He's a little too old for that, I'm afraid, though he's anxious enough. But he left for Paris the day he wrote this. He ought to be here now, for he would, most likely, get off ahead of the mail, which, sometimes, seems slower than molasses."

"That's right!" exclaimed Jack, with such energy that Tom asked:

"What's the matter? Haven't you heard from Bessie lately?"

"Oh--that!" murmured Jack, but Tom noticed that his friend blushed under his coat of tan. "Go on," Jack said, a moment later, "tell me about your father. Is the French government going to give him a big order for his stabilizer, now that we got that paper away from that sneak of a Tuessig?"

"Well, I guess dad's trip here has something to do with his aeroplane device, but he hints in his letter about something else. He said he didn't want to write too much for fear a spy might get hold of the information. But you know my father is an expert on ordnance matters and big guns, as well as in other lines of fighting."

"That's so, Tom. He certainly is a wonder when it comes to inventing things. But what do you suppose his new mission is?"

"I can't quite guess. But it is for the service of the Allies."

"And you say he's on his way to Paris now?"

"He ought to be there by this time," Tom answered. "I'm going to see if I can't get permission to send a message through, and have an answer from dad. Maybe he might get out here to see us."

"Or we could go in and meet him."

"Not for a week. You know we just came back from leave, and we won't be over our tour of duty for seven days more. But I can't wait that long without some word. I'm going to see what I can find out."

Tom and Jack, like all the other American fliers, were in high favor with the French officers. In fact every aviator of the Allied nations, no matter how humble his rank, is treated by his superiors almost as an equal. There is not that line of demarcation noticed in other branches of the service. To be an aviator places one, especially in England and France, in a special class. All regard him as a hero who is taking terrible risks for the safety of the other fighters.

So Tom readily received permission to send a message to the hotel in Paris mentioned by his father as the place where Mr. Raymond would stay. And then Tom had nothing to do but wait for an answer.

Nothing to do? No, there was plenty. Both Tom and Jack had to hold themselves in readiness for instant service. They might be sent out on a bombing expedition at night in the big heavy machines, slow of flight but comparatively safe from attack by other aircraft.

They might have the coveted honor of being selected to go out in the swift, single Nieuports to engage in combat with some Hun flier. To become an "ace"--that is a birdman who, flying alone, has disposed of five enemies--is the highest desire of an aviator.

Tom and Jack, eager and ambitious, were hoping for this.

Again, in the course of the day's work, they might be selected to go up in the big bi-motored Caudrons for reconnoissance work. This is dangerous and hard. The machines carry a wireless apparatus, over which word is sent back to headquarters concerning what may be observed of the enemy's defenses, or a possible offensive.

Often the machines go beyond the range of their necessarily limited wireless, and have to send back messages by carrier pigeons which are carried on the craft.

By far the most dangerous work, however, is that of "_relage_" or fire control. This means that two men go up in a big machine that carries a large equipment. Their craft is heavy and unwieldy, and has such a spread of wing surface that it is not easily turned, and if attacked by a German Fokker has little chance of escape. A machine gun is carried for defense.

It is a function of those in the machine to send word back to the battery officers of the effect of the shots they are firing, that the elevation and range may be corrected. And those who go out on "_relage_" work are in danger not only from the fire of the enemy's batteries, but often, also, from their own.

Tom and Jack had their share of danger and glory during the week they were on duty following the receipt of the two pieces of news. They went up together and alone, and once, coming back from a successful trip over the enemy's lines, Tom's machine was struck by several missiles. His cheek was cut by one, and his metal stability control was severed so that his craft started to plunge.

Tom thought it was his end, but he grasped the broken parts of the control rod in one hand, and steered with the other, bringing his machine down behind his own lines, amid the cheers of his comrades.

"And I'm glad to be back, not only for my sake, but for the sake of the machine. She's a beauty, and I'd have hated like anything to set fire to her," remarked Tom, after his wound had been dressed.

He referred to the universal practice of all aviators of setting fire to their craft if they are brought down within the enemy lines, and are not so badly injured as to prevent them from opening the gasoline tank and setting a match to it. This is done to prevent the machine, and often the valuable papers or photographs carried, from falling into the hands of the enemy.

The end of the week came, the last of seven anxious days, and it was time for Tom and Jack to be relieved for a rest period. And the days had been anxious because Tom had not heard from his father.

"I hope the vessel he was coming on wasn't torpedoed," said Tom to his chum. "He's had more than time to get here and send me some word. None has come. Jack, I'm worried!" And Tom certainly looked it.

Chapter III

On To Paris

Those were the days--and they had been preceded by many such--when travel across the Atlantic was attended with great risk and uncertainty. No one knew when a lurking German submarine might loose a torpedo at a ship carrying men, women and children. Many brave and innocent people had found watery graves, and perhaps suffered first a ruthless fire from the German machine guns, which were even turned on lifeboats! So it was no wonder that Tom Raymond was worried about his father.

"It's queer we can't get any word from the authorities in Paris," remarked Jack, as he and his chum were speculating one day on what might have happened.

"Yes, and that helps to bother me," Tom admitted. "It isn't as if they weren't trying, for the officers here have done all they can. They've gotten off my messages, but they say there is no reply to them."

"Then it must mean that your father, if he is in Paris, hasn't received them."

"Either that, Jack; or else he doesn't dare reply."

"Why wouldn't he dare to, Tom?"

"Well, I don't know that I can give a good reason. It might be that he is on such a secret mission that he doesn't want even to hint about it. And yet I can't understand why he doesn't send me at least a message that he has arrived safely."

As Tom said this he looked at his chum. The same thought was in the mind of each one:

Had Mr. Raymond arrived safely?

That was what stirred Tom's heart. He knew the danger he and Jack had run, coming across to do their part in flying for France, and he well realized that the Germans might have been more successful in attacking the vessel on which his father had sailed, than they had the one which had carried Tom and Jack.

"Well, what are we going to do?" asked Jack of his chum. "You know we arranged, when we should get our leave, to go back to that pretty little French village, which seemed so peaceful after all the noise of battle and the roar of the aeroplane engines."

"Yes, I know we planned that," said Tom, reflectively. "But, somehow, I feel that I ought to stay here."

"And not take our relief?"

"Oh, no. We'll take that," decided Tom. "We must, in justice to ourselves, and those we work with. You know they tell us an airman must always be at his best, with muscles and nerves all working together. And a certain amount of rest and change are necessary, after a week or so of steady flying. So we'll take our rest in order to be in all the better shape to trim the Fritzies. But I was thinking of staying right here."

"And not go back into the country?" asked Jack.

Tom shook his head.

"I'd like to stay right here until I get word from my father," he said. "He may send a message at any time, and he knows I am stationed here. Of course I could send him word that we're having a little vacation, and give him our new address.

"But the mails are so mixed up, and the telegraph and telephone systems are so rushed, that he might not get it. So I think the best thing will be to stay right here where I'll be on hand to get it the moment word comes. But don't let me keep you, Jack. You can go, if you want to."

"Say, what do you think I am?" cried his chum. "Where you stick, I stick! We'll both wait here for word from your father. I have a sort of feeling that he is all right."

"Well, to tell you the truth, I suppose he is. But, at the same time, I'm worried. I can't explain it, but I have a sort of sense that he is in danger."

"Not if he is in Paris, Tom. The German's haven't gotten within striking distance of that city yet, in spite of their boasts--the boasts of the Kaiser and of the Crown Prince."

"No, if dad were in Paris I'd feel that he was comparatively safe. But first I want to know that he is. And yet, even if he has put up at that house in the Rue Lafayette, where he said in his letter he'd stay, there may be some danger."

"Danger in Paris? What do you mean, Tom?"

"Well, Paris has been bombed from the air, you know."

"True, Tom. But, say! we've almost come to disregard such mild things as that from the Huns, haven't we?"

"Well, we'll just stay right on here," decided Tom. "I don't mean to say that we'll stay around our hangar all the while, but we'll keep in touch, throughout the day, with the communication headquarters. Dad may send a message at any time, and I want to get it as soon as it arrives."

Jack could understand his chum's feelings, and so the Air Service boys, who, some time previous, had sought and received permission to go back several kilometers into the country for a rest, announced that they would stay on at the aerodrome.

Nor did they lack excitement. The place where they were stationed was a busy one. For every twenty pilots and observers there are detailed about one hundred men as helpers. There are cooks, photographers, mechanics of various sorts, telephone, telegraph and wireless operators, orderlies and servants.

Of these Tom and Jack had their share, for it is the business of an airman to fly and fight, and he does nothing except in that line. He is catered to and helped in every possible way when not in the air. He has some one to wait on him, to look after his machine, and to attend to his hurts, if he is unlucky enough to get any. Of course each flier goes over, personally, his own craft, but he has oilers and mechanics to do all the detail work.

"Well, there they go!" exclaimed Tom to Jack one morning, the second of their "vacation," as they observed a number of "aces" about to go up and search above the clouds for some Hun to attack.

"Yes, and I wish I was with them!" said Jack.

"Waiting isn't much fun," agreed his chum. "I'm sure I can't understand why dad doesn't send some word. If this keeps up much longer--Say, Jack, look at Parla!" he suddenly cried. "What's the matter with him?"

Jack looked. The men, in their machines, had started off to get momentum for a rise into the air. But there had been a rain and the ground was soft, which kept down the speed. All the pilots seemed to get off in fairly good shape except one, Parla by name, who had only recently secured the coveted designation of "ace."

And then occurred one of those tragedies of flying. Whether he was nervous at taking a flight in such distinguished company, or whether something went wrong with Parla's machine never would be known.

He was the last in the line, and as it was rather misty he might have been anxious not to lose sight of his companions. He did not take a long enough run, and when he reached the end of the field he was not high enough to clear the line of hangars that were in front of him.

Some one shouted at him, not stopping to realize that the noise of the motor drowned everything else in the ears of the pilot.

The luckless man tried to make a sharp turn, to get out of danger. One of his wing tips caught on the canvas tent, or hangar, and in another instant there was a crash and a mass of wreckage. From this, a little later, poor Parla was carried.

But the others did not stay, for though the shadow of death hovered over the Escadrille, the business of war went on.

After three days Tom and Jack could not stand it any longer. They begged for permission to go up into the air. It was granted, though officially they were still on leave. Ascending together in a Caudron, on a photographing assignment, they were attacked by two swift German Fokkers.

Tom worked the gun, and to such good effect that he smashed one machine, sending it down with a crash, and drove the second off. So other laurels were added to those the boys already had.

"If this keeps on we'll be soon wearing the chevrons of sergeants," said Jack, as they landed.

"Well, I'd almost give up hope of them to hear from dad," announced Tom. "I'm going to see if some word hasn't come."

But there was no message. Still the strange silence continued, and Tom and his chum did not know whether Mr. Raymond had reached Paris or not. Through his own captain, Tom appealed to the highest authority at the Escadrille, asking that a last imploring message be sent to the address in the Rue Lafayette.

This was done, and then followed another day of waiting. At last Tom said:

"Jack, I can't stand it any longer! This suspense is fierce!"

"But what are you going to do about it?"

"I'm going to Paris! That's what! We'll go there and find my father if he has arrived. If he hasn't--well, there is still some hope."

"Go to Paris!" murmured Jack.

"Yes. It's the only place where I can make uncertainty a certainty. Come on, we'll go to Paris!"

Chapter IV

Suspicions

Tom Raymond started across the field toward headquarters. Jack followed, but there was a strange look on the latter's face.

"I don't see how you're going to Paris," remarked Jack, at length. "Do you mean we're to go in separate machines, or together?"

"Oh, nothing like that!" exclaimed Tom. "We won't go in machines at all. We'll go by train, if we can get one, or by motor."

"But you're heading for the Escadrille Headquarters office, and--"

"We've got to get official permission to go," explained Tom. "We can't rush off, whenever we like, as we used to go fishing together."

To his captain Tom explained matters more fully than he had done before. In effect he related the fact of having received the letter, stating that Mr. Raymond had started for Paris, presumably to engage in some work for the French government, or at least for the Allies. Whether he had arrived or not, and, in the former case, to ascertain why he had not sent some word to his son, was the object of Tom's quest.

"I've tried and tried, from this end, to get in touch with him," explained Tom; "but something seems to happen to my messages. I know they leave here all right, but after that they are lost. Now I have an idea that there is so much going on in Paris--so much necessary war work--that the ordinary lines of communication are choked. But if I could go to the capital in person I could soon find out whether my father was at the address he gave."

"And you want, do you, to go together?" asked the kindly French captain, smiling at Tom and Jack.

"We'd like to go," said Tom.

"And go you shall. I will write the necessary order. You have done well, and I understand you have some days of leave coming. To them I shall add more. But come back to me," he added, as he filled out the pass form. "Come back. We need you Americans now more than ever!"

"We'll come back," promised Tom. "All I want to go to Paris for is to find out about my father."

"Ah, I envy you," said the captain softly. "Both in the possession of a father, who must be proud to have such a son as you, and also because you are going to Paris. It is the most beautiful--the most wonderful--city in the world. And to think--to think that those barbarians would sack her! Ah, it is terrible!" and with a sad nodding of his head, following the shaking of an avenging fist toward the German lines, he waved Tom and Jack an adieu.

The two Air Service boys lost little time in making their preparations to leave for the French capital. They had to get certain passes and papers, and they wished to say good-bye to some of their comrades in arms. For, more than any other branch of the service, is aviation uncertain as to life or death. Tom and Jack well knew that some, perhaps many, of those who wished them "_au revoir_," and "_bonne chance_," would not be alive when they returned. And Tom and Jack might not return themselves. True, their chances were comparatively good, but the fortunes of war are uncertain.

And so, after certain preliminaries, Tom and Jack, their pet machines in the hangars, left behind their beloved comrades and were taken by motor to the nearest railway station. There they secured their tickets and took their places to wait, with what patience they could, their arrival in Paris.

The train was well filled with "_permissionnaires_," or soldiers on leave for a few days of happiness in the capital, and at certain stations, where more got on, the rush was not unlike that at a crowded hour in some big city.

"I see something good," remarked Jack, as they sat looking out at the scenery, glad, even for a brief moment, to be beyond the horrors of war.

"What?" asked his companion.

"There's a dining-car on this train. We sha'n't starve."

"Good enough, I almost forgot about eating," said Tom. "Now that you speak of it, I find I have an appetite."

They ate and felt better; and it was as they were about to leave the dining-car to go back to their places, that Jack nudged Tom and whispered to him:

"Did you hear what he said?"

"Hear what who said?"

"That man just back of you. Did you have a good look at him?"

"I didn't, but I will have," said Tom, and, waiting a moment so as not to cause any suspicion that his act was directed by his chum, Tom turned and looked at the person Jack indicated. He beheld a quietly dressed man, who seemed to be alone and paying attention to no one, eating his lunch.

"Well, what about him?" asked Tom. "I don't see anything remarkable about him, except that he's a slow eater. I admit I bolt my food too much."

"No, it isn't that," said Jack in a low voice. "But don't you think he looks like a German?"

Tom took another casual glance.

"Well, you might find a resemblance if you tried hard," he answered. "But I should be more inclined to call him a Dutchman. And when I say Dutchman I mean a Hollander."

"I understand," remarked Jack. "But I don't agree with you in thinking that he may be from Holland. Of course men of that nationality have a right to go and come as they choose, where they can, but I don't believe this chap is one."

"Why not?"

"Because I heard him mutter something in German."

"Well, lots of Hollanders can speak German, I have no doubt. I can splutter a few words myself, but not enough to hurt me. I began to pick up some from the prisoners, after we had that experience with Potzfeldt, when we realized that even a little knowledge of the Hun's talk, much as we hate him, would be of service. And so you think you heard this fellow speak German?" asked Tom, as he pretended to tie his shoe lace, to make an excuse for pausing.

"I'm sure I did," said Jack.

"What did he say?"

"Something about wishing he had a plate of _metzel suppe_. Of course I don't guarantee that pronunciation, but--"

"Oh, it'll do," said Tom, graciously. "Well, there's nothing very suspicious in that, though. I might wish for some _wienerwurst_, but that wouldn't make me a German spy."

"No. But take one other thing and you'll have to admit that there is some ground for my belief."

"What's the other thing, old top?" asked Tom, in imitation of some Englishmen.

"He was making drawings of the railroad line," asserted Jack.

"How do you know?"

"I saw him. He pretended to be looking at the _carte de jour_, and I caught a glimpse of a sheet of paper on which he was making certain marks. I'm sure he was sketching out something about the railroad, for use, maybe, in a future air raid."

"Nonsense!" exclaimed Tom. "As a matter of fact, I don't doubt that the German secret agents know every foot of ground in and about Paris. They must have maps of this railroad the same as the French have of some of Germany's, only you've got to hand it to the Huns! They certainly went into this thing well prepared the more discredit to us, in a way. But are you sure of what you say, Jack?" he added, after a moment's thought.

"Positive! I'm sure that man is a German spy, masking as a Hollander or possibly a Swiss. He's sighing for some of his country's good cooking--though that's one of the few good things about it--and he's making some sort of a map."

Tom thought over the matter a moment. The man did not appear to notice the two chums.

"I'll tell you what we can do," Tom said. "We'll soon be in at the Gare de l'Est, and we can tip off some of the officers around there. They can follow this fellow, if they think it's worth while."

"Well, I think it's worth while," said Jack. "If that fellow isn't a spy I'm a Dutchman!"

As Jack spoke the man looked up and full at the two lads, almost as if he had heard the words.

Chapter V

The Bombardment Of Paris

"There, Jack! what did I tell you? I win! You lose, and it's me for a fine dinner at your expense! You lose! Do you hear?"

Tom Raymond, with a hearty laugh, clapped his chum on the shoulder, and seemed mirthfully excited over something. As for Jack Parmly he looked first at his chuckling comrade and then at the man he suspected of being a German spy. The latter, who had glanced keenly at the boys, with something akin to anger on his face, now was plainly puzzled.

"Do you understand?" demanded Tom in a loud voice, which attracted the attention of many in the car. But a look at the two, showing them to be Americans and, therefore, to the French mind, capable of any eccentricity, seemed to make matters right. Most of the diners resumed their meals.

"See what I mean, Jack?" went on Tom. "You lose! Understand?"

"No, I don't understand," was the low-voiced and somewhat puzzled answer.

"Then for the sake of your gasolene tank _pretend_ that you do!" fiercely whispered Tom in his chum's ear. "Play up to my game! Don't you see that fellow's suspicious of us? He thinks we've been talking about him. I win, do you understand?"

"Oh, yes," answered Jack, and then, in a louder tone, intended to allay suspicion on the part of the suspect, he added: "You win all right, Tom! I'll buy the dinner. I didn't think the train would get in so soon! It's one on me all right!"

And then, laughing and talking in seeming carelessness, as though they had not a thought in the world but the friendly wager they had made, they went back to their coach.

"That was a narrow squeak," observed Tom. "He was getting suspicious all right, and in another moment might have made an indignant demand of the guard that we cease observing him. It might have made trouble for us. We're not members of the secret police, remember."

"Well," remarked Jack, "he might have made trouble for us, but I could do the same for him. I'd let fall a hint about the map of the railway he was sketching."

"You mean all right, Jack, but I don't believe your plan would work. If that fellow really is a German spy, which I doubt, he'd destroy the map, if he made one, the moment he thought himself in danger."

"Maybe you're right, Tom," agreed his chum, a bit dubiously. "But I certainly think there is something wrong about that man."

"Maybe you think he is Carl Potzfeldt, disguised, Jack."

"No, nothing like that. Though I wouldn't be surprised if he happened to be friendly with that sneaking spy. And, speaking of Potzfeldt, Tom, though he isn't by any means a pleasant subject, do you know we are soon to be in Paris where--"

"Where Bessie and her mother are, you mean. You're right, old chap, I haven't forgotten that, and I'll wager one chance for promotion that you haven't forgotten it either."

Jack's blush was sufficient answer to his friend.

"I couldn't quite understand what you meant, Tom, by talking so suddenly and loudly about you winning and me losing," went on Jack, as they got their baggage ready, for the train was about to enter the Paris station.

"That was camouflage, Jack, pure and unadulterated camouflage," answered Tom with a laugh. "I had to do something in a hurry to get that fellow's gaze off us, or he might have made a scene, and we don't want that. But if I had made a wager with you about the time, I'd have won, for here we are, right on the dot, which is unusual in these days, I believe."

"You said something, Tom. But what are we going to do about our spy?"

"Well, if you insist that's what he is, I think the best thing would be to notify some secret service official. There must be plenty of them around the station. Every passenger, before he leaves the station, has to have his papers stamped by the military authorities. Then's your chance to tip them off about this chap."

"I'll do it, Tom. I'm not going to lose any chances of putting German enemies out of the way."

It was about five o'clock when the train pulled into the Gare de l'Est, and the passengers, including many soldiers on leave, prepared for the joys of Paris. Tom and Jack, proceeding as did the others to the place designated for the official stamping of papers, found a chance to tell their suspicions to an officer, and to point out the man Jack suspected.

"The matter shall be attended to," said the military official, treating the information with the utmost respect, and evidently considering it of more importance than Tom imagined would be attached to it. "We are greatly indebted to you, not only because you are of our beloved aviators, but because you also think to do this for France--to protect her from enemies within as well as from those who are without. France thanks you, gentlemen!" and the aged officer saluted the two young men as though he considered them his equals.

"Well, now that's off our minds we can get down to the real business that brought us to Paris," suggested Tom. "And that's to find my father--if he's here. After that we can look up Bessie and her mother, if you like, Jack."

"Of course I'll be glad to do that, Tom, and I should think that you--"

"Oh, of a surety, yes, as a Frenchman would say. I'll be happy also, to see our friends again, but I know Bessie will consider--"

"Oh, drop it, will you?" begged Jack, for he could see that his chum was about to start to rally him about the girl.

"Then," went on Tom, "the first thing to do, in my opinion, is to get to this address in the Rue Lafayette where dad said he would make his headquarters, and see why he hasn't answered any of my messages. When I once see him, and know he's all right, I'll feel better."

"Even capable of eating that dinner you claim to have won from me?" asked Jack.

"Of course."

The two Air Service boys had the satisfaction of seeing the "tip" they gave acted on, for as they left the station they observed the officer to whom they had reported, detailing a man in plain clothes, evidently one of the secret police, to follow the man they had watched in the dining car.

"We can leave the rest to the military," said Tom. "And now let's get to where we're going."

"Hadn't we better arrange for hotel accommodations, or to stop at a pension?" asked Jack. "You know Paris is crowded now, even in war times, and we've got to stay here all night, even if we learn that your father hasn't yet arrived."

"That's so," agreed Tom. "Maybe we had better get a place to bunk first."

It would not have been an easy task had they not worn the uniforms of aviators. But once these were noted, they were welcomed with smiles, and though at the first place they applied there was no room, the proprietor busied himself to such advantage that the boys were soon settled in a big double room with a fine view of a busy section of Paris.

On every side was seen evidence of the joy and satisfaction felt at the showing made by the progress of the United States in her war programme.

The stars and stripes were seen floating from many staffs, mingled with the tricolor of France and the English union jack. That Uncle Sam had at last gotten beyond the bounds of patience with a ruthless and sneaking enemy and was making energetic warfare against him was welcome news to those who had so long borne the unequal brunt of battle.

"Americans? Ah, everything that I have is yours!" the hotel proprietor told Tom and Jack. "You have but to ask. And now come, I will show you the way to the cellar."

"But we don't care to see the cellar," remarked Tom in wonder. "No doubt it is a very fine one, monsieur," he added in his best French, which was nothing to boast of. "No doubt it is most excellent, but we don't care for cellars."

"Ah, I know, but it is for protection in case of an air raid that I show it to you. It is there we all take shelter. There have been raids, and there will be more. It is well to be prepared. It is a well-protected cellar."

"Oh, well, that's different," observed Jack. "Come on, Tom, we'd better learn the best and quickest route to the basement. No telling when we might want to use it."

They descended with the proprietor and saw that he had arranged the cellar with a false roof of beams, on top of which were sand bags. In case a bomb was dropped on the hotel or in its vicinity the cellar would offer almost certain protection.

The boys arranged for a stay of at least a week in Paris, having told the proprietor their errand to the capital. By the time they had finished their dinner they found it was too late to set out in search of Mr. Raymond, as in the changed, war-time Paris little could be done in the evening. So Tom and Jack retired to their room and their bed.

"Are you going right to the Rue Lafayette?" asked Jack of his chum, the next day.

"Yes, and if we can't get any news of him there we'll appeal to the military authorities. I have a letter of introduction to persons high in authority from our captain."

The boys hailed a taxicab and gave the chauffeur the necessary directions. They were bowling along through the beautiful streets of Paris, noting on all sides the warlike scenes, and their thoughts were busily occupied, when they suddenly became aware that something had happened.

Like a thunderbolt from a clear sky there sounded a terrific explosion, and at no great distance. The concussion shook the ground, and they could feel the taxicab tremble under the shock, while the chauffeur instantly threw on all brakes, making the machine skid dangerously.

"What is it? What's the matter?" yelled Jack.

"Airship raid most likely!" shouted Tom. "Boches are dropping bombs on Paris! Oh, where's our cellar, Jack?"

The taxicab driver jumped down and opened the door.

"You had best alight, gentlemen," he said. "You must seek shelter."

"Is it an airship raid?" asked Tom.

"No, there is not an airship in sight. No such alarm has been sounded by the police. I fear the bombardment of Paris by the Germans has begun!"

Chapter VI

The Rue Lafayette Ruins

Tom Raymond and Jack Parmly alighted from the taxicab more quickly than they had gotten in. The chauffeur was anxiously scanning the sky. Excited men, women and children were rushing about, and yet it was not such excitement as might be caused by the first shelling of the beautiful city. It was more, as Tom said afterward, as though the populace had been taken by surprise by a new method in the same kind of warfare, for an occasional German Zeppelin or a bombing aircraft had, before this, dropped explosives. To these the French had become as much accustomed as one ever can to such terrible means of attack.

But this was different. There was no sign of a Hun aircraft, and, as the chauffeur had said, no police warning had been sounded.

"What is it?" asked Jack.

"It is a bombardment, that is all I know," replied the taxicab driver. He spoke in French, a language which the two boys used fairly well, though, as has been said, their accent left much to be desired.

"You had best seek shelter until it is over," went on the man. "I shall do so myself." He seemed to pause suggestively, and Jack handed him some money.

"_Merci_," he murmured, and an instant later was careening down the street at full speed.

"He isn't losing any time," said Jack.

"No. And perhaps we hadn't better, either. Where'd that shell fall?" asked Tom.

"I don't know, but it must have been somewhere about here, judging by the noise. Look, the crowd's over that way," and he pointed to the left.

It was true. Careless of the danger of remaining in the open, men, and women, too, as well as some children, were rushing toward the place where, undoubtedly, the shell from the German gun had fallen.

"Might as well take it in," suggested Jack. "I don't want to crawl down into a cellar or a subway quite yet, even if there's one around here; do you?"

"No," answered Tom, "I don't. Go on, I'm with you."

They followed the throng, but could not resist the impulse to gaze upward now and then for a possible sight of another shell, which, they half hoped, they might observe in time to run for shelter. But of course that would have been out of the question. However, quiet succeeded the din of the explosion, which had been close to the spot where the taxicab had stopped and the boys had alighted.

Following the crowd, Tom and Jack came to a side street, and one look down it showed the havoc wrought by the German engine of death. The shell, of what kind or calibre could not be even guessed, had fallen on top of an establishment where a number of women and girls were employed. And many of these had been killed or wounded. There were heart-rending scenes, which it is not good to dwell upon. But, even in the terror and horror, French efficiency was at the fore.

Ambulances were summoned, a guard was thrown about the building, and the work of aiding the injured and tenderly carrying out the dead was begun. A vast and excited throng increased in size about the building that had been hit and there was much excitement for a time.

Tom and Jack managed to get to a place where they could get a view of the havoc wrought to the structure itself, and the first thing that impressed them was mentioned by Jack, who said:

"They didn't use a very big shell, or there wouldn't have been such comparatively slight material damage done."

"The force was mostly expended inside the building," suggested Tom.

"Even so, if it had been a big shell, the kind they fired at Verdun and Liege, there'd be a crater here big enough to put a church in. As it is, only the two top stories are wrecked."

"That's right," agreed Tom. "I wonder what sort of explosive they are using? Must have been one from a bombing aeroplane."

"No, monsieur," interrupted a _gendarme_ who was standing near. "Pardon, for speaking," he went on, with a salute, "but there was no airship observed over Paris at all. The shell came out of the clear sky."

"But it couldn't have," insisted Jack, in reply to this policeman. "If the Germans are firing on Paris they must have some place from which to shoot their gun. Either on the ground or from an airship."

"It was not an airship," insisted the _gendarme_. "Excuse me for insisting this to one who is in the air service," and he pointed with pride to the uniform the boys wore, "but I have seen several air raids, and I know! There was no airship seen, or I would have blown the alarm," and he motioned to his whistle which he carried for that purpose.

"It could have come from an immense airship, so high up as to be beyond observation," suggested Jack. "That's possible. Probably the Germans didn't want to be bombarded themselves by aircraft guns here, and they flew high."

The police officer shook his head. He was not convinced.

"But, man, how else could it be?" asked Tom, in some heat. "The Huns have to rest their gun somewhere, and you--Say, Jack!" he suddenly exclaimed, his face paling slightly, "you don't suppose they have broken through, do you?"

"Through our lines about Paris? Never!" cried the police officer. "They shall not pass! Our brave soldiers have said it, and they will maintain it. They shall not pass!"

"And yet," mused Tom, as he looked at the rescue work going on, "what other explanation is there? It's a bombardment of Paris all right, by German shells. If they don't come from an aeroplane, high up, they must come--"

His words were drowned by another great concussion, but farther off. The ground trembled, but there was no sign of flying debris.

"Another!" cried the _gendarme_. "There goes the gun again!"

"I didn't hear any gun," observed Jack. "What we heard was the explosion of the shell. Look up, Tom, and see if there's a Hun plane in sight. If there is, pity we haven't our machines right now."

The boys carried, slung over their shoulders, powerful binoculars, and with these they swept the sky. Others about them were doing the same. By this time the most seriously injured had been carried to the hospitals, and the dead had been removed, while those only slightly hurt, as well as those in the factory not at all injured, were telling their experiences. The second explosion seemed to create great terror.

"There isn't a sign of a hostile plane," said Tom, as he swept the sky with his glasses.

"I can't see any either," observed Jack. "And yet--"

There sounded the unmistakable roar of an aircraft's propeller.

"There she is!" cried some one.

But it was one of the first of a series of French planes that had hastily ascended to search the heavens for a sight of the supposed German craft that had dropped the bombs.

"What a chance we're missing!" murmured Jack.

"Yes," agreed Tom. "But they're going to have some flight before they locate that Hun. There isn't so much as a speck in the sky except the French craft."

"Let's go and see where that other explosion was," suggested Jack, when they had observed several of the French planes scurrying to and fro over the city, climbing higher and higher in search of the enemy.

"I'm with you," announced Tom. "I wonder what dad thinks of this?"

"It'll be something new for him," said Jack. "He'll have a good chance to see how his stabilizer works, if they're using it on these planes here. And maybe he can invent a better one."

"Perhaps," returned Tom. "But, Jack, do you know I'm worried about one thing."

"I have more than that on my mind, Tom. There are mighty serious times all about us, and it's terrible to think of those poor women and girls being killed like rats in a trap. I'd just like to be in my plane, and with a full gun, and then have a go at the Hun who did this."

"So would I," agreed Tom, as they made their way out of the crowd and in the direction in which many of the populace were hurrying to go to the scene of the second explosion. "But, Jack, do you know I shouldn't be surprised to learn that the shell was not from an airship at all."

"Where would it be from then?"

"The Germans may have massed such a lot of troops at some point opposite the French lines, that they have broken through and have brought up some of their heavy guns."

Jack shook his head.

"I don't believe they could do it," he said. "You know the nearest German line is about seventy miles from Paris. If they had started to break through, and had any success at all, the news would have reached here before this. And reinforcements would be on the way. No, it can't be. There must be some other explanation."

"But what is it?" asked Tom. "They've got to get nearer than seventy miles to bombard Paris. You know that."

"I don't think I really _know_ anything about this war," said Jack simply. "So many strange, things have happened, so many old theories have been discarded, and so many new things have been done that we don't know where we are."

"Well that's true. And yet how could the Germans get near enough to bombard Paris without some word of it coming in?"

"I don't know. But the fact remains. Now let's get to where the second shell fell. Maybe we can see a fragment of it and--"

Once again the words were interrupted by an explosion. This time it was closer and the shock was greater.

"That's the third!" cried Jack.

"Yes," added Tom, looking at his watch, "and it's just half an hour since the first one fell. That indicates they're firing every fifteen minutes. Jack, there's something weird about this."

"You're right. That last one came rather close, too. I wonder where it fell?"

A man, passing them, running in a direction away from the sound of the last explosion, heard Jack's question. He paused long enough to say; "That shell fell in Rue Lafayette. Several buildings are in ruins. Many have been killed! It is terrible!"

"Rue Lafayette!" gasped Jack. "That--"

"That's where my father is supposed to be staying!" exclaimed Tom. "Come! We must see what happened!"

Chapter VII

Tom'S Father

With anxious hearts the Air Service boys ran on. There was no need to ask their way, for they had but to follow the throng toward the scene of the most recent exhibition of the Hun's frightfulness and horror.

As they drew near the Rue Lafayette, where Mr. Raymond had said he intended to stay while in Paris, the boys were halted by an officer on the outskirts of the throng.

"Pardon, but you may not go farther," he said, courteously enough. "There is danger. We are about to sound the alarm so that all may take to shelter. The Boches are raiding Paris again."

"We know it," said Tom. "But it is no idle curiosity that takes us on."

"No?" politely questioned the policeman.

"No. I am seeking my father. He wrote to me that he would stop in the Rue Lafayette, and I have not heard from him since. I was told that the last shell fell in that street."

"It did," assented the officer, "and it demolished two houses and part of another. Many were killed and injured."

"Then I must see if my father is among them!" insisted the young aviator.

"Pardon, monsieur, it is not possible. I have my instructions, and--"

He stopped, and for the first time seemed to become aware of the uniforms worn by Tom and Jack. Then the officer saluted as though proud to do it.

"Ah," he murmured. "Of the Lafayette Escadrille! You may go where you will. Only I hope it is not into danger," he said, as he drew aside for them to pass. "Pardon, I did not at first sense who you were. France owes you much, messieurs. Keep your lives save for her!"

"We will," promised Tom, as he hurried on, followed by Jack.

They came to the head of the street they sought, and, looking down it, beheld ruins greater than they had seen before. As the officer had said, two buildings had been completely demolished, and a third partly so, the wreckage of all mingling. And amid these ruins police and soldiers were working frantically to get out the injured and remove the dead, of whom there was a sad number.

Tom's face was white, but he kept his nerve. He had been through too many scenes of horror, had been too near death too often of late, as had his chum, to falter now, even though his father might be among those buried in the wreckage caused by the German shell.

"Do you know what number your father was to stop at?" asked Jack.

"Yes, I have his letter," Tom answered. "I'm afraid, Jack, it was in one of those buildings that have been blown apart."

"No, Tom!"

"I'm afraid so. But, even at that, he may have had a chance for his life. He may have been out, or, after all, he may not have arrived yet. I'm not going to give up hope until I have to."

"That's the way to talk, old man. I'm with you to the last."

They pressed on, and populace and officers alike gave way before them as they saw the uniforms.

"We've got to help!" declared Tom. "We must pitch in, Jack, and lend a hand here. The soldiers seem to be in charge. Let's report to the commanding officer and offer our services."

"But your father?"

"That's the best way to find him if he's in those ruins. Let us help get the unfortunates out. I hope I don't find him, but I must make sure."

Making their way through the press of people, which, under order of the police and military authorities, had begun to disperse in some small measure, Tom and Jack reported to the officer in charge, giving him their names and rank, at the same time showing their papers.

"We want to help," the lads told him.

"And I ask no better," was the quick response. "There are dead and dying under that pile. They must be gotten out."

And then began heart-rending scenes. Tom and Jack did valiant work in carrying out the dead and dying, in both of which classes were men, women and children.

The German beasts were living up to the mark they had set for themselves in their war of frightfulness.

Each time a dead or injured man was reached, to be carried out for hospital treatment or to have the last sad rites paid him, Tom nerved himself to look. But he did not see his father, and some small measure of thankfulness surged into his heart. But there were still others buried deep under the ruins, and it would be some time before their bodies, dead or alive, could be got out.

As the soldiers and police worked, on all sides could be heard discussions as to what new form or manner of weapon the Germans were using thus to reach Paris. Many inclined to the theory that it was a new form of airship, flying so high as to be not only beyond ordinary observation, but to be unreachable by the type of planes available at Paris.

"If we could only find a piece of the shell we could come nearer to guessing what sort of gun fired it," remarked Tom, as the two Air Service boys rested a moment from their hard, terrible labors.

"Do you mean if it was dropped from an airship it wouldn't have any rifling grooves on it?" asked Jack.

"That's it. A bomb, dropped from an aeroplane, would, very likely, be only a sort of round affair, set to explode on contact or by a time fuse. But if it was a shell fired from a long-range gun, there might be enough of it left, after the explosion, to observe the rifling."

"There isn't a gun with a range long enough to reach Paris from the nearest German lines, unless they have broken through," said Jack.

"Well, the last may have happened; though I should think we'd have got some word of it in that case. There'd be fierce fighting if the Germans tried that, and we'd rush reinforcements out in taxicabs as the Paris soldiers went out once before."

"Do you think then," asked Jack, as they went back, after their brief respite, to their appalling labors, "that they have a gun long enough to fire from their nearest point, which is about seventy miles from this city?"

"I don't know what to think," remarked Tom. "It seems like a wild dream to speak of a gun that can shoot so far; and yet reality is over-topping many wild dreams these days. I'm going to reserve judgment. My chief concern now, though of course I'm not going to let it interfere with my work, is to find my father. If he should have been in here, Jack--"

Tom did not finish, but his chum knew what he meant, and sympathized with his unexpressed fear for the safety of Mr. Raymond.

Digging and delving into the ruins, they brought out the racked and maimed bodies, and there was more than one whose eyes were wet with tears, while in their hearts wild and justifiable rage was felt at the ruthless Germans.

Ten had been killed and nearly twice that number wounded in the third shell from the Hun cannon.

From a policeman Tom learned that one of the two buildings that had been demolished was the number given by Mr. Raymond as the place he would stay.

"The place he picked out may have been full, and he might have gone somewhere else," said Tom. "We've got to find out about that, Jack."

"That's right. I should think the best person, or persons, to talk to would be the janitors, or '_concierges_,' as they call 'em here."

"I'll do that," responded Tom.

Aided by an army officer, to whom the boys had recommended themselves, not only by reason of their rank, but because of their good work in the emergency, they found a man who was in charge of all three buildings as a renting agent. Fortunately he had his books, which he had saved from the wreck.

"You ask for a Monsieur Raymond," he said, as he scanned the begrimed pages. "Yes, he was here. It was in the middle building he had a room."

"In the one that was destroyed?" asked Tom, his heart sinking.

"I regret to say it--yes."

"Then I--then it may be all up with poor old dad!" and Tom, with a masterful effort, restrained his grief, while Jack gripped his chum's hand hard.

Chapter VIII

Where Is Mr. Raymond?

Tom Raymond, having gone through a hard school since he began flying for France, soon recovered almost complete mastery of himself. The first shock was severe, but when it was over he was able to think clearly. Indeed the faculty of thinking clearly in times of great danger is what makes great aviators. For in no other situation is a clear and quick brain so urgently needed.

"Well, I'm sure of one thing, Jack," said Tom, as they walked away from the fateful ruins. "Of those we helped carry out none was my father. He wasn't among the injured or dead."

"I'm sure of that, too. Still we mustn't count too much on it, Tom. I don't want you to have false hopes. We must make sure."

"Yes, I'm going to. We'll visit the hospitals and morgues, and talk with the military and police authorities. In these war times there is a record of everybody and everything kept, so it ought to be easy to trace him."

"He arrived all right, that's settled," declared Jack. "The agent's record proves that."

"Yes. I'd like to have a further talk with that agent before we set out to make other inquiries."

This Tom was able to bring about some time later that day. The agent informed the lad that Mr. Raymond, contrary to his expectations, had arrived only the day before. Where he had been delayed since arriving in Europe was not made clear.

"But was my father in the building at the time the shell struck here?" asked Tom. "That's what I want to know."

Of this the man could not be certain. He had seen Mr. Raymond, he said, an hour or so before the bombardment, and the inventor was, at that time, in his room. Then he had gone out, but whether he had come back and was in the house when the shell struck the place, could not be said with certainty.

But if he had been in his apartment there was little chance that he had been left alive, for the explosion occurred very near his room, destroying everything. Tom hoped, later, to find some of his father's effects.

"There is just a chance, Jack," said the inventor's son, "that he wasn't in his room."

"A good chance, I should say," agreed the other. "Even if he had returned to his room, and that's unlikely, he may have run out at the sound of the first explosion, to see what it was all about."

"I'm counting on that. If he was out he is probably alive now. But if he was in his room--"

"There would be some trace of him," finished Jack.

"And that's what we've got to find."

The police and soldiers were only too willing to assist Tom in his search for his father. The ruins, they said, would be carefully gone over in an endeavor to get a piece of the German shell to ascertain its nature and the kind of gun that fired it. During that search some trace might be found of Mr. Raymond.

It did not take long to establish one fact--that the inventor's body was not among the dead carried out. Nor was he numbered with the injured in the hospitals. Careful records had been kept, and no one at all answering to his description had been taken out or cared for.

And yet, of course, there was the nerve-racking possibility that he might have been so terribly mutilated that his body was beyond all human semblance. The place where his room had been was a mass of splintered wood and crumbled masonry. There was none of his effects discernible, and Tom did not know what to think.

"We've just got to wait," he said to Jack, late that afternoon, when their search of the hospitals and morgues had ended fruitlessly.

Meanwhile the French airmen had been scouring the sky for a sight of the German craft that might have released the death-dealing bombs on the city. But their success had been nil. Not a Hun had been sighted, and one aviator went up nearly four miles in an endeavor to locate a hostile craft.

Of course it was possible that a super-machine of the Huns had flown higher, but this did not seem feasible.

"There is some other explanation of the bombardment of Paris, I'm sure," said Tom, as he and Jack went to their lodgings. "It will be a surprise, too, I'm thinking, and we'll have to make over some of our old ideas and accept new ones."

"I believe you're right, Tom. But say, do you remember that fellow we saw in the train--the one I thought was a German spy?"

"To be sure I remember him and his _metzel suppe_. What about him? Do you see him again?" and Tom looked out into the street from the window of their lodging.

"No. I don't see him. But he may have had something to do with shelling the city."

"You don't mean he carried a long-range gun in his pocket, do you, Jack?" and Tom smiled for the first time since the awful tragedy.

"No, of course not. Still he may have known it was going to happen, and have come to observe the effect and report to his beastly masters."

"He'd be foolish to come to Paris and run the chance of being hit by his own shells."

"Unless he knew just where they were going to fall," said Jack.

"You have a reason for everything, I see," remarked Tom. "Well, the next time we go to headquarters we'll find out what they learned of this fellow. You know we started the secret service agents on his trail."

"Yes, I know. Well, I was just sort of wondering if he had anything to do with the bombardment of Paris. You've got to look for German spies now, even under your bed at night."

The boys felt they could do nothing more that day toward finding Mr. Raymond. A more detailed and careful search of the ruins might reveal something. Until this was accomplished nothing could be done.

They ate a late supper, without much in the way of appetites, it must be confessed, and then went out in the streets of Paris. There seemed to be few signs of war, aside from the many soldiers, and even the bombardment of a few hours earlier appeared to have been forgotten. But of course there was grief in many hearts.

It was early the next morning, when Tom and Jack were getting ready to go back to the ruins in the Rue Lafayette, that, as they left their lodgings, they heard in the air above them the familiar sounds of aeroplanes in flight, and the faint popping of machine guns, to which was added the burst of shrapnel.

"Look!" cried Jack. "It's a battle in the air. The Huns are making another raid. Now we'll see how they bomb the city."

But it did not turn out to be that sort of raid. The German craft were flying low, apparently to get a view of the havoc wrought the day before. Possibly photographs were being taken.

But the French aeroplanes were ready for the foe, and at once arose to give battle, while the anti-aircraft guns roared out a stern order to retreat. It was a battle above the city and, more than once, Tom and Jack wished they could be in it.

"We'll have to get back to our hangars soon," mused Tom, as they watched the fight. "We can't be slackers, even if I can't find my father," he added bravely.

The French planes were too much for the Germans, and soon drove them back beyond the Hun lines, though perhaps not before the enemy aviators had made the observations desired.

"Well, they didn't see much," remarked Jack. "As far as any real damage was done to Paris it doesn't count, from a military standpoint."

"No, you're right," agreed Tom. "Of course they have killed some noncombatants, but that seems to be the Boche's principal form of amusement. As for getting any nearer to the capture of Paris this way, he might as well throw beans at the pyramids. It's probably done for the moral, or immoral, effect."

And this seemed to be the view taken of it by the Paris and London papers. The method of bombardment, however, remained a mystery, and a baffling one. This was a point the military authorities wished to clear up. To that end it was much to be desired that fragments of the shell should be found. And to find them, if possible, a careful search was made, not only in the ruins of the Rue Lafayette, but at the other two places where the explosions had occurred.

In no place, however, was a large enough fragment found to justify any conclusive theories, and the Parisians were forced to wait for another bombardment--rather a grim and tense waiting it was, too.

But the careful search of the Rue Lafayette ruins proved one thing. The body of Tom's father was not among them, though this did not make it certain that he was alive. He may have been totally destroyed, and this thought kept Tom from being able to free his mind of anxiety. He dared not cable any news home, and all he could do was to keep on hoping. These were anxious days for him and Jack.

Their leave of absence had been for a week only, but under the circumstances, and as it was exceptionally quiet on their sector, they were allowed to remain longer. Tom wanted to make a more thorough search for his father, and the police and military authorities helped him. But Mr. Raymond seemed to have completely disappeared. There was no trace of him since the agent for the Rue Lafayette buildings had seen him leave his room just prior to the falling of the shell.

Jack inquired about the man he suspected of being a German spy. The secret service men had him under observation, they reported, but, as yet, he had not given them any cause to arrest him. They were waiting and watching.

Meanwhile active preparations were under way, not only to discover the source of the bombardment of Paris, but to counteract it. Extra anti-aircraft guns, of powerful calibre, were erected in many places about the city, and more airmen were summoned to the defense.

As yet there had been no resumption of the bombardment, and there were hopes that the German machine, whatever it was, had burst or been put out of commission. But on the second day of the second week of the boys' stay in Paris, once more there was the alarm and the warning-from the soldiers and police, and again came that explosion.

The bombardment of Paris was being renewed!

Chapter IX

Various Theories

Two things were at once apparent to Tom and Jack as they hurried out of their _pension_. One was that the people of Paris were not seeking shelter after the warnings as quickly as they had done at first, and the other was that there was evident curiosity on all sides to see just what damage would be done, and from which direction it would come. With an almost reckless disregard for their safety, if not for their lives, the Parisians fairly flocked out of doors to see the results of the Huns' bombardment. It was in vain that the police and military urged them to seek safety in cellars or the places provided.

This time only one shell fell near enough to Tom and Jack to make the explosion heard, and that was so faint as to indicate that it was some distance off. What damage had been done could only be guessed at.

"But we'll find out where it is, and go take a look," said Jack.

"Maybe it'll hit right around here if we stay," suggested his chum.

"Well, I'm not taking that chance," Jack went on. "Let's find out where it landed this time."

This they could do through their acquaintance with the military authority of the district where they were then staying. A telephonic report was at once received, giving the quarter where the shell had landed. It had fallen in one of the public squares, and though a big hole had been torn in the ground and pavement, and several persons killed and wounded, no material damage had been done. As for any military effect of the shell, it was nil.

The firing was done in the early evening hours, and Tom and Jack learned that, almost to the second, the shots were fifteen minutes apart.

There was one theory that an underground passage had been made in some manner to within a comparatively few miles of Paris, and from that point an immense mortar sent up the shells in a long trajectory.

Another theory was that traitors had let the Germans through the French lines at a certain place, so they could get near enough to Paris to bombard it.

And of course the gigantic airship theory had its adherents.

But, for a time at least, no one would admit the possibility of a gun with range sufficient to shoot into Paris from the nearest German lines. The range, sixty-odd miles, seemed too great for practical belief, however nicely it might work out in theory.

"And you must remember that the gun, if gun it is, couldn't be in the very first German line," said Tom, who had studied ordnance. "It must be at least ten miles back, to allow for sufficient protection from the French guns. That would make it shoot about seventy-two miles, and I don't believe any gun on earth could do it!"

"Neither do I," added Jack. "We've got to dope out something else. But this isn't finding your father, Tom."

"I know it, and I don't mind admitting I'm clean discouraged about him, Jack. If he's alive why doesn't he send me some word? He must know where I am, and, even if he doesn't know I'm in Paris, they would forward any message he might send to our aeroplane headquarters."

"That's right. But what are you going to do about it?"

"I hardly know. He may still be in Paris, but it's such a big city that it's hard to find him. Then, too, I'm thinking of something else."

"What's that, Tom?"

"Well, dad may not want us to know where he is."

"Why in the world would he want such a thing as that?"

"Well, he might be followed, or bothered by spies. Perhaps he has come over to do some special work for the French or English army people. Maybe a spy was after him just before the big German gun wrecked his Rue Lafayette house. He may have considered this a good chance to play dead, and that's why he doesn't send some word to me."

"That's a good theory. But it isn't very comforting."

"No, but there isn't much comfort in war times. We've got to make the best of it."

"I guess you're right, Tom. Now do you want to go look at the latest work of the Hun?"

"Might as well. The bombardment seems over for the night."

"I wonder why it is they don't fire after dark."

"Probably afraid of giving the location of their cannon away by the flashes. They'd be seen at night; but during the day, if they used smokeless powder, or a smoke screen in case they can't get smokeless powder for such a big gun, it would be hard to locate the place where the shots come from. So we're comparatively safe after dark, it seems."

Later this was not to prove to be the case, but it was when Tom spoke.

The boys went to the section of the city in which the last shells had fallen. While comparatively little damage had been done, a number of persons had been killed and injured, children among them. Some fragments of the shells were picked up, but not enough to make certain any particular theory in regard to the gun.

"But if it's a gun, where could it be placed?" queried Tom of an officer. "The Germans haven't broken through, have they?"

The French officer shook his head.

"No. And please God they will never get through," he said. "But there is a gun somewhere, I am sure of that."

"Do you mean to say within ten or fifteen miles of Paris?" Jack wanted to know.

"I can not be sure. It is true there may have been traitors. We have them to contend with as well as spies. But our line is intact, and at no point along it, near enough to it to fire into Paris from an ordinary gun, can the Germans be found."

"Then it must be an extraordinary gun," suggested Jack.

"It may well be--perhaps it is. Yet, as I said, there may have been traitors. There may be a gun concealed somewhere closer to Paris than we dream. But we shall find it, messieurs! Who knows? Perhaps you may be the very ones yourselves to locate it, for we are depending on you soldiers of the air."

And it was not long before this talk came back to Tom and Jack with impressive recollection.

And meanwhile the bombardment of Paris went on, usually during the late afternoon or early morning hours--never at night, as yet.

Yet with all the frightfulness of which the unscrupulous Huns were capable, it was impossible to dampen for long the spirits of the French. Soon they grew almost to disregard the falling shells from the hidden German gun. Of course there were buildings destroyed, and lives were lost, while many were frightfully maimed. But if Germany depended on this, as she seemed to, to strike terror to the hearts of the brave Frenchmen the while a great offensive was going on along the western front, it failed. For the people of Paris did not allow themselves to be disheartened, any more than the people of London did when the Zeppelins raided them.

Indeed one Paris paper even managed to extract some humor out of the grim situation. For one day, following the bombardment, a journal appeared with "scare" headlines, telling about eleven "lives" being lost. But when one read the account it was discovered that the lives were those of chickens.

And this actually happened. A shell fell on the outlying section and blew up a henhouse, killing nearly a dozen fowls and blowing a big hole in the ground.

There were other occasions, too, when the seemingly superhuman bombardment was not worth the proverbial candle. For the shells fell in sections where no damage was done, and where no lives paid the toll. Once a shell went through a house, passing close to an aged woman, but not hurting her, to explode harmlessly in a field near by.

And it was with such accounts as these that the Paris papers kept up the spirits of the inhabitants. Meanwhile the Germans kept firing away at quarter-hour intervals, when the gun was in action.

"I wonder if there is any chance of us getting in at the game?" questioned Jack of Tom one night.

"I shouldn't be surprised. As that officer said, they'll have to depend on the aircraft to locate the gun, I'm thinking."

"And you think we have a chance?"

"I don't see why not," replied Tom. "We've been off duty long enough. I'd like to get back behind the propeller again, and with a drum or two of bullets to use in case we sight a Hun plane. Let's go and send word to our captain that we've had enough of leave, and want to go out again."

"All right. But what about your father?"

"Well, I don't know what to say," answered Tom. "I'm about convinced that he wasn't killed, or even hurt, in any of the bombardments of Paris. But where he is I don't know. I guess, as a matter of duty to France, I'll have to let my private affairs go and--"

At that instant there sounded an explosion the character of which the two boys well knew by this time.

"The big gun again!" cried Jack.

"Yes, and they're firing after dark!" added Tom. "This may be just the chance the airmen have been waiting for--to locate the piece by the flashes. Come on out and see what's doing!"

Together they rushed from their room.

Chapter X

The "Dud"

Much the same sort of scene was going on in the streets of Paris as Tom and Jack had witnessed when first the populace realized that they were under fire from a mysterious German cannon. There was the initial alarm--the warnings sounded by the police and soldiers, warnings which were different from those indicating a Zeppelin or aircraft raid, and then the hurry for cover.

But it was noticeable that not so many of the people rushed for a secure hiding place as had done so at first.

"They're not so afraid of the big gun as they were," observed Jack, as he hurried along with his chum.

"No. Though it's just as well to be a bit cautious, I think. The people of Paris are beginning to lose fear because they see that the German shells don't do as much damage as might be expected."

"You're right there, Tom," said Jack. "The shells are rather small, to judge by the damage they do. I wonder why that is?"

"Probably their gun, or guns, can't fire any larger ones such a long distance, or else their airships can't carry 'em up above the clouds to drop on the city."

"Then you still hold to the airship theory?"

"Well, Jack, I haven't altogether given it up. I'm open to conviction, as it were. Of course I know, in theory, a gun can be made that will shoot a hundred miles, if necessary, but the cost of it, the cost of the charge and the work of loading it, as well as the enormous task of making a carriage or an emplacement to withstand the terrific recoil, makes such a gun a military white elephant. In other words it isn't worth the trouble it would take--the amount of damage inflicted on the enemy wouldn't make it worth while."

"I guess you're right, Tom. And yet such a gun would make a big scare."

"Yes, and that's what the Germans are depending on, more than anything else."

"But still don't you think the French will have to do something toward silencing the gun?"

"Indeed I do! And I haven't a doubt but the French command is working night and day to devise some plan whereby the gun can be silenced."

"There go the aviators now, out to try to find the big cannon," observed Jack, as he gazed aloft.

Soaring over Paris, having hastened to take the air when the signal was given, were a number of planes, their red, white and blue lights showing dimly against the black sky. They were off to try to place the big gun, if such it was, or discover whether or not some Hun plane was hovering over the city, dropping the bombs.

As Jack and Tom hastened on, in the wake of the crowd, which was hurrying toward the place where the latest shells had fallen, again came a distant explosion, showing that the gun had been fired again.

"Fifteen-minute interval," announced Tom, looking at his watch. "They're keeping strictly to schedule."

"Night firing is new for the big gun," said Jack. "I do hope they'll be able to locate the cannon by the flashes."

"It isn't going to be easy," asserted Tom.

"Why not?"

"Because you can make up your mind if the Germans were afraid to fire the piece at night at first for fear of being discovered, and if now they are firing after dark, they have some means of camouflaging the flash. In other words they have it hidden in some way."

"Well, I suppose you're right. But say, Tom, old man! what wouldn't I give to be able to be up in the air with those boys now?" and Jack motioned to the scouts who were flitting around in the dark clouds, seeking for that which menaced the chief city of the French nation.

"I'd like to be there myself," said Tom. "And if this keeps up much longer I'm going to ask permission for us to go up and see what we can do."

"Think they'll let us?"

"Well, they can't any more than turn us down. And we've got to get at it in a hurry, too, or we'll have to report back at our regular station. We aren't doing anything here, except sit around."

"No, we must get busy, that's a fact," said Jack. "It's about time we downed some Hun scout, or broke up one of their 'circus' attacks. I've almost forgotten how a joy stick feels."

A "joy stick" is a contrivance on an aeroplane by the manipulation of which the plane is held on a level keel. If the joy stick control is released, either by accident (say when the pilot is wounded in a fight), or purposely, the plane at once begins to climb, caking its passenger out of danger.

Once the joy stick is released it gradually comes back toward the pilot. The machine climbs until the angle formed is too great for it to continue, or for the motor to pull it. Then it may stop for an instant when the motor, being heavier, pulls the plane over and there begins the terrible "nose spinning dive," from which there is no escape unless the pilot gets control of his machine again, or manages to reach the joy stick.

"Well, we'll have to get in the game again soon," said Tom. "But what do you say to taking a taxi? This explosion is farther than I thought."

Jack agreed, and they were soon at the place where the last German shell had fallen--that is as near as the police would permit.

A house had been struck, and several persons, two of them children, killed. But, as before, the military damage done was nothing. The Germans might be spreading their gospel of fear, but they were not advancing their army that way.

As Tom and Jack stood near the place where a hole had been blown through the house, another explosion, farther off, was heard, and there was a momentary flare in the sky that told of the arrival of another shell.

For a few seconds there was something like a panic, and then a voice struck up the "Marseillaise," and the crowd joined in. It was their defiance to the savage Hun.

A few shots were fired by the Germans, but none of them did much damage, and then, as though operating on a schedule which must not, under any circumstances, be changed, the firing ceased, and the crowds once more filled the streets, for it was yet early in the night.

The next morning the boys went to report, as they did each day, expecting that they might be called back to duty. They also found, after being told that their leave was still in effect, that some of the aviators who had gone up the night before, to try to locate the German gun, were on hand.

"Now we can ask them what they saw," suggested Jack.

"That's what we will," assented Tom.

But the airmen had nothing to report. They had ascended high in search of a hostile craft carrying a big gun, but had seen none.

They had journeyed far over the German lines, hoping to discover the emplacement of the gun, if a long range cannon was being used. But they saw nothing.

"Not even flashes of fire?" asked Tom.

"Oh, yes, we saw those," an aviator said. "But there were so many of them, and in so many and such widely scattered places, that we could not tell which one to bomb. We did manage to hit some, though with what effect we could not tell."

"Then the German gun is still a mystery," observed Tom.

"It is. But we shall discover it soon. We will never rest until we do!"

So more and new and different theories continued to be put forth regarding the big cannon, if such it was. Ordnance experts wrote articles, alike in London, Paris, and New York, explaining that it was possible for a cannon to be within the German lines and still send a shell into the French capital. But few believed that it was feasible. The general opinion was that the gun was of comparative short range, and was hidden much nearer Paris than the sixty or seventy-odd miles away, beyond which stretched the German line of trenches.

Meanwhile Tom, though making careful inquiries, had learned nothing of his father. He did not feel it would be wise to cable back home, and ask what the news was there.

"It might spoil dad's plans if I did that," said Tom to his chum, "and it would worry the folks in Bridgeton to know that I haven't yet seen him in France. No, I'll just have to wait."

And wait Tom did, though there is no harder task in all the world.

It was one morning, after a night bombardment on the part of the Germans, that Jack, who had been out for a morning paper, came rushing into the room where Tom was just awakening.

"Great news, old man! Great!" cried Jack, waving the paper about his head.

"You mean about a victory?" asked Tom.

"No, not exactly, though it may lead to that. And it isn't any news about your father, I'm sorry to say. It's about the German gun. A 'dud' fell last night."

"A 'dud'?" repeated Tom, hardly sensing what Jack said.

"Yes, you know! A shell that didn't explode. Now they have a whole one to examine, and they can find out what sort of gun shot it. This paper tells all about it. Come on! Let's go for a look at the 'dud'!"

Chapter XI

A Monster Cannon

Tom, dressing hastily, read the account in the Paris paper of the fall, in an outlying section of the city, of one of the German shells that failed to explode. It was being examined by the military authorities, it was stated, with a view to finding out what sort of gun fired it, so that measures might be taken to blow up the piece or render it useless to the enemy.

"That sounds good to me," said Tom, as they made a hasty breakfast. "This is getting down to a scientific basis. An unexploded shell ought to give 'em a line on the kind of gun that fired it."

"The only trouble," said Jack, "is that the shell may go off when they are examining it."

"Oh, trust the French ordnance experts not to let a thing like that happen," said Tom. "Now let's go to it."

It was fortunate that Tom and Jack wore the uniforms that had so endeared them to France, or they might have had difficulty in gaining admittance to the bureau where the unexploded shell was under process of investigation. But when they first applied, their request was referred to a grizzled veteran who smiled kindly at them, patted them on the shoulders, called them the saviors of France, and ushered them into the ordnance department, where special deputies were in conference.

"Yes, we have one of the Boche shells," said an officer, who spoke English fluently, for which Tom and Jack were glad. They could speak and understand French, but in a case like this, where they wanted a detailed and scientific explanation, their own tongue would better serve them.

"And can you tell from what sort of gun it comes?" asked Tom.

"It was fired from a monster cannon," was the answer. "That is a cannon not so much a monster in bore, as in length and in its power to impel a missile nearly eighty miles."

"Can it be done?" asked Jack.

"It has been done!" exclaimed Major de Trouville, the officer who was detailed to talk to the boys "It has been done. That is the gun that has been bombarding Paris."

"But, from a military standpoint," began Tom, "is it--"

"It is utterly useless," was the quick answer. "Come, I will show you the shell."

He led them to an apartment set aside for the testing of explosives and working out ordnance problems, and there on a table, around which sat many prominent French officials, was the German shell--the "dud," as Jack had called it.

"The charge has been drawn," explained Major de Trouville, "so there is no danger. And we have determined that the manner in which shots reach Paris from a distance of from seventy to eighty miles is by the use of a sub-calibre missile."

"A sub-calibre?" murmured Tom.

"Yes. You know, in general, that the more powder you use, and the larger the surface of the missile which receives it, the greater distance it can be thrown, providing your angle of elevation is proper."

The boys understood this much, in theory at least.

"Well," went on the major, "while that is true, there is a limit to it. That is to say you could go on using powder up to hundreds of pounds in your cannon, but when you get to a certain point you have to so increase the length of the gun, and the size of the breech to make it withstand the terrific pressure of gases, that it is impracticable to go any further. So, also, in the case of the shell. If you make it too large, so as to get a big surface area for the gases of the burning powder to act upon, you get your shell too heavy to handle.

"Now of course the lighter a missile is, the farther it will go, in comparison to a heavy one with the same force behind it. But you can not get lightness and sufficient resistance to pressure without size, and here is where the sub-calibre comes in."

"In other words the Germans have been firing a shell within a shell," broke in another officer.

"Exactly," said Major de Trouville. "The Germans have evolved a big gun, that is big as regards length, to enable the missile they fire from it to gain enough impulse from the powder. But the missile would be too large to travel all the way to Paris. So they use two. The inner one is the one that really gets here and explodes."

"What becomes of the outer?" asked Jack.

"It is a sort of container, or collar, and falls off soon after the shell leaves the big gun. If you will imagine a sort of bomb shell being enclosed in an iron case, the whole being put in a gun and fired, you will better get the idea. The outer case is made in two or more pieces, and soon after it is shot out it falls away, leaving the smaller missile to travel on. But here is where the cunning of the invention comes in. The smaller missile has all the impetus given the larger one, but without its weight. In consequence it can travel through eighty miles of atmosphere, finally reaching Paris, where it explodes."

"Wonderful!" exclaimed Jack.

"And yet it is merely the adaptation of an old theory," went on the major. "We have known of the sub-calibre theory for years, but it is not practicable. So we did not try it. The cost is too great for the amount of military damage done. And this shell, as you will see, is composed of two parts, each with a separate explosive chamber, each containing, as we discovered, a different sort of explosive. In this way if one did not go off, the other would, and so set off the one that failed. It is very clever, but we shall be more clever."

"That's right!" chimed in a chorus of fellow officers.

"We'll find the gun and destroy it--or all of them if they have more than one, as they probably have," went on the major.

He showed the boys where the shell had chambers for the time fuses to work, much as in a shrapnel shell, which can be set to go off so many minutes or so many seconds after it reaches its objective point.

"And so the great question is settled by the failure of this shell to explode," went on the major. "As soon as we saw it, and noted the absence of the rifling groove marks, we knew it must have been a sub-calibre matter. The rest was easy to figure out.

"Some of us thought there might be a big airship, stationed high above the clouds, dropping bombs. Others inclined to the theory of a double shell; that is, after one had been fired from the cannon it would travel, say, half way and then explode a charge which would impel another shell toward Paris. A sort of cannon within a cannon, so to speak. But this is not so. Nor did the theory of a shell with a sort of propeller device, like that of a torpedo, prove to be right. It is much simpler--just sub-calibre work."

"And what is going to be done about it?" asked Tom. "I mean how can the monster cannon be silenced?"

"Ah, that is a matter we are taking up now," was the answer of Major de Trouville. "I fancy we shall have to call on you boys for a solution of that problem."

"On us?" exclaimed Jack.

"Well, I mean on the aircraft service. It will be their task to search out this great German cannon for us, to enable our gunners to destroy it. Or it may be that it will have to be bombed from an aeroplane."

"That's the task I'd like all right!" cried Tom, with shining eyes.

"Same here!" echoed Jack. "Do you suppose we'll get a chance?" he asked eagerly.

"You may," was the reply. "It may take all the resources of our airmen to destroy this terror of the Germans. But it will be done, never fear!"

"_Vive la France!_" cried his companions, and there was a cheer in which Tom and Jack joined.

And so a part of the secret was discovered. It was a monster cannon that was devastating Paris. A great gun, the construction of which could only be guessed at. But it must be destroyed! That was certain!

Chapter XII

For Perilous Service

Tom and Jack spent some little time looking at the strange German shell. It was of peculiar construction, arranged so that the two explosive charges would detonate together or separately, according as the mechanism was set.

But in this case it had failed to work, and the shell, falling in a bed of soft sand, near some new buildings which were going up, had not been fired by concussion, as might have happened.

"And it was just French luck that it didn't go off," observed Jack.

"That's right," agreed Tom. "If they hadn't had this whole shell to examine they wouldn't know about the big gun."

So all the theories, fantastic enough some of them, about great airships hovering over the beautiful city, and dropping bombs from a great height, were practically disproved.

"Well, now that you have decided it is a big German gun, the next question is, where is it and what are you going to do about it?" observed Tom, for he and Jack had been made so much of by the French officers that they felt quite at home, so to speak.

"Ah, messieurs, that _is_ the question," declared Major de Trouville. "First to find the gun, and then to destroy it. The first we can do with some degree of accuracy."

"How?" asked Tom.

The major went to a large map hanging on the wall of the room. It showed the country around Paris and the various lines as they had been moved to and fro along the Western front, according as the Germans advanced or retreated.

"You will observe," said the major, "that by describing an arc, with Paris as the center of the circle, and a radius of about seventy-five miles, you will include a small sector of the German trenches. Roughly speaking this arc will extend from about Hamegicourt to Conde, both within the German lines, I am sorry to say. Now then, somewhere in this arc, or perhaps back of it, the German gun is placed. Anywhere else where it would be possible for such a monster engine of war to be erected, would bring it too close to our batteries.

"So that gives us the comparative location of the gun," went on the French officer. "But the next question is not so easy to settle--how to get rid of it. As I said, I think we shall have to depend on you airmen."

"Well, we're for the job!" exclaimed Tom.

"I know you are. And it may fall to you, or to your friends. I will talk of that later."

"Have you been able to get any idea of the kind of gun it is, or why it fires at fifteen minute intervals?" asked Jack.

"We have been able to get no really reliable information save that which we deduce by our observations of this shell and from what we know of the location of our own and the German lines," the Major went on. "Up to now our airmen have not been able to penetrate far enough without being attacked, and such few as did get well over toward the Rhine could make out nothing. I have no doubt the gun is well camouflaged."

"And is it true that it doesn't fire at night because the Germans are afraid the flashes will be seen?" asked Tom.

"That may have been the reason at first, but they have fired at night, of late, so they must have some way of concealing the flashes, or perhaps setting off other flashes at the same time so as to confuse our scouts."

"It's going to be some job," murmured Jack.

"You said something," agreed his chum.

They remained talking a little longer, and some of the officers who knew the reason for Tom's visit to Paris, expressed regret that he had no information as yet about his father.

"But take heart," one told him. "He is not dead, or we should have heard of it. Of course he may have fallen into the hands of the Germans, and then we would not know for some time."

"He may have been caught," agreed Tom. "While Tuessig is out of the game on account of his injuries, he may be able to direct Potzfeldt, and that scoundrel would have good reason for trying to get revenge on us."

"Ah, yes, I heard about your rescue of the young lady and her mother," said the major. "It was a brave deed."

"Oh, any one could have done it," said Tom, modestly.

"And have you seen them since they came to Paris?" the major proceeded.

"No, but I wish we could find them!" burst out Jack, and then he blushed at his impetuosity, while Tom murmured something about "Bessie," and Jack promptly told him to hold his tongue.

"Perhaps you may meet them sooner than you expect," went on the French officer.

"Now I wonder what he could have meant by that?" asked Jack, as he and his chum went out, after a final look at the German shell. "Does he know where they are?"

"It wouldn't be surprising, seeing that Mrs. Gleason is probably in Red Cross work, and Bessie may be helping her. We should have looked them up before," went on Tom. "But what with searching for my father, and the excitement about the bombardment, I really forgot all about them."

Jack did not say whether he had or not, the chances being that he had, more than once, thought of Bessie Gleason.

During the next two days the monster cannon continued to shoot shells at intervals into Paris. Some did considerable damage, as any shell would do in a great city, and many unfortunates were killed. But there was no reign of terror such as, undoubtedly, the Boches hoped to create. Paris remained calm, and there were even jokes made about the cannon. It was called a "Bertha" and other names, the former referring to Bertha Krupp, one of the owners of the great German ordnance works.

Word was given out that the French gunners on the front were trying to reach the big gun with their missiles. But as they were firing blindly it could not be said what havoc had been wrought.

"But, sooner or later, we'll get the range, and get within striking distance," said one of the French officers. "Then we'll show them a trick or two."

"Have the aviators done anything toward trying to find the gun?" asked Tom. "I mean anything more."

"We are perfecting our plans for the flying corps," was the answer. "Perhaps you shall know more in a few days."

"Well, I hope we'll be here when the fun begins," said Tom, grimly. "We've got another extension of leave, and I'm going to ask the police now, to co-operate with the military in seeking my father."

"I think that will be a wise plan. We will give you all the help we can."

But the quest for Mr. Raymond seemed a hopeless one, and as no confirmation could be had of his death or injury, the idea gradually became fixed in the minds of Tom and Jack that he had been made a German prisoner.

"If that is so, and I can get any trace of him, I'll go over the Rhine to get him back," snapped Tom.

"And I'll go with you!" declared his chum.

It was a few days after they had inspected the German "dud," and the boys were wondering what new developments might take place, the shelling of Paris meanwhile continuing at intervals, that one evening the boys were visited in their lodgings by Major de Trouville.

"Is there any news?" eagerly asked Tom, for he guessed that the French officer would not be paying a merely social call. Those were the strenuous days when such things had passed.

"Well, yes, news of a sort," was the answer. "But what I came to find out was whether you were so taken with these lodgings that you could not be induced to move."

"To move!" exclaimed Jack.

"Yes. Have you found anything unhealthful here?"

"Why, no," replied Tom, wonderingly. "We like it here. The landlord couldn't be nicer, and we're in a good location."

"Nevertheless, I fear I shall have to ask you to change your quarters," went on the major, and by the quizzical smile on his face the boys guessed that there was something in the wind.

"Let me ask you another question," went on the French officer. "Have you been annoyed since you have been here?"

"Annoyed? How?" inquired Tom.

"By unwelcome visitors, or by strangers."

The boys thought for a moment.

"There's one chap who lives in the same building here, whom we've seen on our staircase several times," said Jack, slowly. "Once I saw him pause at our door with a key, as though he were going to enter, but he heard me coming, and, muttering that he had taken too much wine and was a bit hazy in his memory, he went on upstairs."

"I thought as much," the major said. "Was the man you speak of familiar to you?"

"No, I can't say that he was," replied Jack, and Tom nodded his acquiescence. "I never saw him before."

"Oh, yes you have," and the major smiled.

"I have? Where?"

"On the train, coming into Paris."

"You mean the German spy?" cried Jack.

"The same," answered the Frenchman. "That's just what he is, and he is spying on you. Now, in view of what is going to happen, we don't want that to go on. So I have come to ask you to change your lodgings, and I think I can take you to one that will be most agreeable to you both."

"But what does all this mean?" asked Tom. "Is there----"

"There is 'something doing' as you say so picturesquely in the United States," interrupted the major. "I have come to tell you that you are to undertake a most perilous mission!"

Chapter XIII

The Spy

Tom Raymond and Jack Parmly looked first at one another and then at the major. He had been smiling at their wonderment, but he was now serious, and regarded them gravely.

"Do you mean we have to do something to help catch this spy?" asked Tom.

"I'd like a hand in that!" exclaimed Jack. "I saw him first--he's my meat!"

"Well, get him if you can, boys," said the Frenchman. "But I did not come here to talk so much about him as about yourselves. The spy is a danger and a menace, but we know him and if he goes too far we can put out our hands and drag him back.

"No, what I referred to is more dangerous than merely trying to catch a spy at his sneaking work. I will tell you." The major suddenly left his seat near the window of the boy's room, and quickly opened the door leading to the hall. The passage was empty.

"I rather thought there might be an eavesdropper," the major explained. "I was followed here, though I don't believe the spies know my mission. However, it is best to be careful. With your permission I'll pull down the shade. There may be spies stationed across the street who, with powerful glasses, might look through the window and gather something of what we say by reading our lips. It has been done."

"The Germans don't leave much untried," commented Tom. "But what is it you want us to do, if it isn't trying to trail the spy?"

The major motioned them to draw closer to him, and then, leaving the door into the hall open, so that he could note the approach of any one, he whispered:

"You are to be two members of a picked company of air scouts who are to go out, discover the big German gun, and destroy it!"

"Whew!" whistled Tom, after a moment of thought during which he and Jack exchanged quick glances.

"Well?" asked the officer. "How does that strike you? I believe that is another of your captivating terms?"

"It's all to the good!" exclaimed Jack. "What say, Tom? We'll take that on, won't we?"

"Well, I should say!" was the enthusiastic rejoinder. "When do we start to--"

"Hush!" cautioned the major. "Not so loud. Though we have taken every precaution, there may be spies unseen by us. We had better talk no more about it here."

"Then let's go to our new lodgings, if we are to move," suggested Tom. "Will it be safe to talk there?"

"I think so," the major said. "At least you will be among friends. Not that your landlord here is not a true Frenchman; but he can not control the actions of those to whom he lets lodgings. You will be better where you are going. Then you accept the mission?" he asked in another whisper.

"Sure thing!" answered Tom, while Jack nodded his assent. "The sooner the quicker!"

"I do not quite get that," the major confessed with a smile. "But I think I gather your meaning. Now if you will proceed to this address," and he handed Tom a small slip of paper, "you will find a comfortable lodging, and you will be among friends."

"How soon can we start on--on this mission?" asked Tom.

"It will be better not to refer to it directly," the officer said. "Talk as little about it as you can. But you shall go as soon as the arrangements can be made. You will be notified."

"And what about seeing our friends--Mrs. Gleason?" asked Jack.

"Are you sure its _Mrs._. Gleason you want to see?" inquired Tom.

"Oh, cut it out!" advised Jack with a blush.

"You may see them soon now," the major told him with a smile. "And I hope you'll soon have good news of your father," he added to Tom.

"I hope so, too. The suspense is telling on me."

"I should think it would. Now don't leave this bit of paper about with the address of your new lodgings on. Better commit it to memory, and then destroy the sheet. We want, if possible, to prevent the spy from knowing where you have gone. I will call a taxicab for you. You can be packed soon, I suppose?" he questioned.

"Within a half hour," answered Jack. "But say, won't that spy be on the watch, and won't he learn from the taxicab driver where we have gone?"

"Not from _this_ taxicab driver," was the smiling answer. "He is one of our best secret service men. But treat him as you would an ordinary chauffeur. You may even give him a tip, and he will not be offended," and once more the major smiled.

Tom and Jack, having made sure they remembered the address given them, destroyed the paper, and then proceeded to get ready to move. Meanwhile Major de Trouville took his departure, promising to keep in communication with the Air Service boys.

Punctual to the half hour a taxicab appeared at the door. The boys obeyed the instructions they had received, and looked out to make sure the spy was not on hand. If he was, he was well concealed, for they did not see him.

"Though I suppose he's somewhere around," said Jack.

"Well, maybe we can fool him," suggested Tom. "We're going quite on the other side of Paris."

They made sure that, as far as could be told by observation, there was no one resembling the spy around the place or in the street in front, and then got into the cab with their baggage. The chauffeur seemed not to know them, but Tom thought there was just the slightest wink of one eye, as though to indicate that the game was going well.

Their cab was driven out along the Boulevard Ragenta, past the Gare du Nord, and across the Boulevard de Rochechquart to a small street running off the Rue Ramey, and there the cab stopped in front of a small but neat-looking house.

"Quiet enough neighborhood," remarked Jack, as they got down, and Tom tipped the cabman for the benefit of any spies who might be looking.

"Yes, I guess we can get some sleep here, if the big gun doesn't keep us awake," agreed Tom.

On the way they had passed several places where the havoc of the "Bertha" was noticeable.

Tom and Jack seemed to be expected, for the porter, who came down to get their bags, did not seem at all surprised to see them. He bade them follow him, and a little later, the cab having chugged off, the boys were settled in a pleasant room, a smiling landlady coming in to see if they wanted anything, and to tell them they could have meals with her at certain hours, or they might dine out as they pleased.

"Your friends will be here shortly," she added.

"Our friends?" questioned Tom.

"Yes," with a nod and a smile. "I was told to say they would be here shortly after you arrived."

"Oh, I guess she means the major and some of the officers will come to see how we are situated, and to tell us more about--the big stunt," said Tom in English to his chum, assuming that "big stunt" would sufficiently disguise to any listening spies, if such there were, the real object that lay before them.

"I suppose that's who she means," agreed Jack, as the landlady, who gave her name as Madame Reboux, withdrew.

The boys were busy unpacking their few belongings, for they had not brought much to Paris, not intending to stay long, when they heard voices in the hall outside their room. And at the tones of a certain voice Tom and Jack started and looked at one another.

"Listen!" exclaimed Tom.

"If I wasn't afraid you'd say I was dreaming, I'd say I knew that voice!" murmured Jack.

"I'd say the same," added Tom.

"Who would you say it was?" his chum challenged.

"Well, for a starter--"

He paused, for the voice sounded more plainly now, and it said:

"Yes, this is the right place, Mother. Oh, do you think the boys are here yet?"

"It surely will be a pleasure to meet them again," said another voice, evidently that of a woman, the other having been a girl's.

"I hope they won't have forgotten us," the girl went on, and at that Jack could no longer keep quiet. He rushed to the door, opened it, and cried:

"Bessie! Is that you?"

"Oh, it's Jack! Mother, here's Jack!" cried the girl, and she and her mother were soon shaking hands with Tom and Jack.

"So, you two were the friends we were soon to see!" exclaimed Tom, as he placed chairs for Mrs. Gleason and her daughter. Or, to be exact, Tom placed a chair for the mother, while Jack got one for Bessie.

"Yes, we were told you would be here," said Bessie's mother. "We did not know you were in Paris until we received word that it would be better for us to change our lodging and come here."

"The same word we received," said Jack. "Say, it's working out mighty queer, isn't it, Tom?"

"Yes, but very satisfactorily, I should say. Things couldn't be nicer. How have you been?" he asked, for he had not seen the girl nor her mother since the sensational rescue from the perfidious Carl Potzfeldt.

"Very well indeed," answered Mrs. Gleason. "Both Bessie and I have been doing Red Cross work. But isn't that great German gun terrible? Oh, how it has killed and maimed the poor women and children! The Huns are fiends!"

"I quite agree with you," said Tom, Jack meanwhile talking to Bessie. "But it isn't doing them the military good they thought it would, and, if all goes well, it may not very long do them any service at all."

"You mean--" began Mrs. Gleason.

But just then Bessie, who had arisen to go to the window to view the street, turned back with a start, and grasped Jack's hand.

"Look! Look!" she whispered, and through the curtains she pointed to a man on the opposite side of the way.

"Do you know him?" asked Jack.

"Know him? Yes, to my sorrow."

"Who is it?" asked Tom.

"The spy!" exclaimed Jack. "The man we saw in the train, and the same fellow who tried to get into our lodgings. In spite of our precautions he has found out where we are."

"I'm not so sure of that," said Tom. "He may not be here for any particular purpose. But do you know him too, Bessie?"

"Yes," the girl answered. "He was in the chateau where mother and I were held prisoners by Potzfeldt. He is a tool in the pay of that spy, and a spy himself!"

"Then we ought to do something!" exclaimed Jack, and he started to rush from the room.

Chapter XIV

With Comrades Again

"Hold on! Wait a minute!" exclaimed Tom, as he caught hold of his chum. "Where are you going?"

"Out to give warning to a policeman or to some army officer about that spy!" exclaimed Jack. "We know him to be such, and now, with Bessie's word that he was with Potzfeldt, it's enough to cause his arrest."

"Yes, maybe it is," agreed Tom, who was a bit more cautious than his impetuous chum. "But if we do that we may spoil the plans of Major de Trouville. Better let matters take their course, Jack. That spy may not know we are here, and again, he may. But if he doesn't, rushing out now would be sure to give the secret away. As it is, there is a chance we may keep it."

Jack, caught midway in his impetuous rush from the room, stood reflectively. What Tom had said to him appeared to make an impression. Then Bessie added her words of advice.

"Yes, Jack," she said, "I think it would be rather rash to go out now and confront that man, or start a chase after him. I know I'm not as experienced as you two famous birdmen," she went on with a smile, "but I've been through some terrible experiences, as almost every girl has in this war zone, and I can do more thinking than I used to. Don't you think it would be wise to wait, Mother?"

"Yes, Bessie," answered Mrs. Gleason, "I do. Our good friends in the military service who told us to come here, must have had some object. Perhaps it was connected with this same man who was so unkind to us in the chateau, and who was certainly a tool of that man I trusted once, but never will again--Carl Potzfeldt!" and she shuddered as she thought of what she had gone through.

"Let him go," she said to Jack. "Perhaps it is just a coincidence that he is passing just as we arrive. Our departure from our last lodgings was made secretly."

"So was ours," said Tom. "And yet I don't see how that spy found us so soon."

"It is that which makes me think it is accidental," observed Mrs. Gleason. "It would be very unwise now to go out, I think."

"All right, then I'll stay in," said Jack with a smile. "Especially as I have such good company. Tell me," he went on, "are you and your mother going to board here?" he asked Bessie.

"Yes," answered Mrs. Gleason. "And though we were told we would meet friends here we could not guess it would be you brave boys."

"Spare my blushes!" laughed Tom.

"Same here," added Jack.

"But what brings you to Paris?" asked Bessie. "I thought you boys were engaging in combats above the clouds."

"We have been fighting, though not during the last two weeks," said Tom. "I had word that my father had come over here, but he never communicated with us, and we came to Paris to look him up. So far we haven't succeeded in finding him," and he gave the details of the visit of himself and his chum to the capital, telling of their first experience during the firing of the big gun.

Bessie and Jack, who seemed to have much to say to one another, peered from behind the curtains out of the window now and then, and Jack at last reported that the spy had passed on, after stopping, apparently, to purchase some fruit at a stand on the street.

"I don't believe he knew we were here," said Bessie.

"Well, it won't do to take any chances," observed Tom. "However, we were not told to remain under cover, so I suppose we can go out when we like."

"Better wait until we get some word from the major," suggested Jack, who was getting some of his chum's caution.

All decided this was best, and the boys spent the rest of the afternoon in getting their room to rights, Mrs. Gleason and Bessie doing the same in their apartment. Mrs. Gleason had temporarily been relieved from Red Cross work to recuperate, she said, as she had been under a great strain.

Toward evening Major de Trouville, or "Trouville," as he democratically liked to be called, arrived, and when told of the sight in the street of the spy, who turned out to be the same man who was one of the captors of Bessie and her mother, the officer said:

"I am not surprised. In fact I rather looked for that, and it is one reason why I wanted to get you four together so you could see the man at the same time.

"There is now no doubt as to his intentions, and the fact that he was here so soon after you arrived proves that there is a 'leak' somewhere. We suspected as much, and I think I know where it is. It is good information to have. Well, boys, did I surprise you?" he asked, smiling.

"You did, indeed, but it was a pleasant surprise," said Jack.

"But when are we going to be allowed to do something to silence that monster cannon?" asked Tom. "It's pleasant to be here, but we are not forgetting there is work to do."

"Nor would I have you forget," said the major. "A number of persons were killed to-day by fire from the long-range gun. We believe, now, that there are two or three of them, as the shots come at closer intervals. It is imperative that something be done, and so I have brought you orders."

"Good!" cried Jack.

"That sounds like business!" commented Tom.

"In regard to your father," went on the major, addressing Jack's chum, "we will be on the watch for him, or any news of him, and, no matter where you are, unless you are captured by the Germans, you shall be informed as soon as possible."

"Is there any chance of being made prisoners?" asked Jack, and it might be noted that he did not use the word "danger."

"There is always that chance for an airman," replied the major. "But when I add that it may be possible that one or both of you will take a flight over the Rhine, you can judge, with the hold Germany has on French possessions, what the danger is."

"Over the Rhine!" exclaimed Tom. "Why, that's a flight of two or three hundred miles from Paris."

"Yes, but with the new type of Italian plane which you may use, it is not impossible in a single flight," said the major. "However, we will talk of that later. Just now I have come to tell you that you are to rejoin your comrades at the Lafayette Escadrille for a time. There arrangements will be made for the perilous venture I spoke of--the silencing of the big guns that are bombarding Paris. I wish you all success, young gentlemen."

"Thanks," murmured Jack.

"We consider it an honor to be picked for such duty," added Tom. "Are any others going to be in the game?"

"Oh, yes. We shall need a picked corps of the best airmen we have, French and Americans, and it will be no easy matter then. The Germans have probably been planning this for a long time, and they, no doubt, have taken every possible precaution against surprise or failure. But with the help of you brave Americans we shall win!"

"That's right!" chimed in Bessie. "Oh, how I wish I were a man!" and she looked enviously at Jack and Tom.

The major gave Bessie and her mother some instructions in regard to their actions should the spy come back, and then told Tom and Jack to prepare to leave Paris the next night.

"Report to your former camp," he said, "and there you will find further instructions waiting for you."

"Well, then as we have to-night, our last one free, let's go to some entertainment," suggested Tom to Bessie and her mother. "We can have supper afterward--not much of a celebration, for these are war times and it won't do to rejoice too much. But we ought to commemorate this meeting somehow."

"That's right!" agreed Jack.

So they went to a little play and had supper afterward in a quiet restaurant. That is, it was quiet until a sudden explosion a few blocks away announced the arrival of another German shell from the big gun, and then there was excitement enough.

Fortunately, however, the shots did little beyond material damage, no one being killed. At the same time, however, there appeared some German planes over Paris, doubtless to observe the effect of the dropping of the long-distance shells, and naturally the French airmen went up to give them combat.

The great searchlights began to play, picking out the hostile craft, and making them targets for the machine guns of the intrepid Frenchmen, and more than one Boche never got back over his lines again, while several Frenchmen found heroes' graves on the soil they had died to defend.

"Oh, if we were only up there helping," said Tom, as he and his friends watched.

"We shall be there very soon," murmured Jack. "And it can't be any too soon for me."

The tide of battle turned in favor of the French, the Hun planes withdrawing as the fire got too hot for them. And soon after that the long-range gun ceased firing.

It was rather a "pull" for Tom and Jack to say good-bye to Bessie and her mother in Paris, but they knew they had to do their duty. Nor would Mrs. Gleason and her daughter have kept the boys back for the world. They realized that the Air Service boys were helping to make the world safe for democracy, as they themselves were doing in their way.

And so Tom and Jack, their mission to Paris, which was the discovery of Mr. Raymond, having failed, went back to the hangars, there to be welcomed by their comrades in arms.

They arrived one morning, just after some planes from a bombing expedition over the German lines returned.

"What luck?" asked Tom of a pilot with whom he had often flown.

"The best, as regards the damage we did," was the answer. "We blew up several ammunition dumps, and put one railroad center out of business for a time. But Louis didn't come back," and the man turned aside for a moment.

"You mean your brother?" asked Jack, softly.

"Yes."

"Perhaps he is only captured," suggested Tom.

"No, his machine caught fire. They got his petrol tank. It's all up with him and La Garde. But we had our revenge. We sprayed the machine that got them until there was nothing left of it. And I'm going out again to-day in a Nieuport. They'll pay a price for Louis!"

Chapter XV

The Picked Squadron

"All ready, Jack?"

"Just a moment, Tom. I want to go over my struts and wires to make sure everything is taut. I don't want any accidents."

"That's right. Got plenty of ammunition drums?"

"All I can carry. I've got some tracer bullets, too."

"That's good. Glad you reminded me of them. I must put in a stock. The last time I went up I wasted a drum before I got my man."

Tracer bullets for aircraft guns, it might be observed, are balls of fire which enable the pilot to see the course his machine gun bullets are taking, so he may correct his fire.

"Well, how about you now?" asked Tom, as he added these useful supplies to his ammunition.

"I guess we're ready to start," replied Jack.

They climbed into their machines, each pilot using a single-seat, swift-flying craft, equipped with a Lewis machine gun. The squadron was going out on patrol duty, and each pilot was to observe what he could behind the German lines, and come back to report--that is if he did not happen, as was too often the case, to be bagged by a German flier. The small, swift machines did not carry the wireless outfit, and no reports could be sent back to headquarters save those the pilot himself came in with.

There was a rattle and a roar as the motors of the ten machines started, and then over the ground they went, "taxi fashion," to get the necessary speed to rise into the air. A moment later all went aloft, and were headed toward the German lines.

Tom and Jack kept as close together as was safe, but it is dangerous for two aeroplanes to approach too closely. If they do, and are not under good control, there may be a suction created that will cause a collision.

"Well, I hope I get one to-day," thought Tom, as he manipulated his "joy stick," so as to send his plane up on a sharp slant. "I want to make good, and then I'll have so much better chance to get after that German gun." And the same thought was in Jack's mind.

The squadron was to remain aloft on a two-hour patrol, that is unless something should occur to make it advisable to remain up longer. The keen eyes of Tom and Jack, as well as those of their companions of the air, were searching for signs of the Hun planes. As yet none were in sight, but it would not be long before they would come out to give battle.

Whatever else may justly be said about the Germans, their airmen are no cowards, and, when conditions are favorable, they seldom decline a chance to combat above the clouds, or lower down. So it could easily be guessed that when Tom, Jack and the others found themselves over the German lines that the Boches would be out in force.

Somewhat off to the left Tom caught sight of a captive German balloon, looming through the mist, and as it is always the desire of a French flier to destroy one of these, thus preventing the observer from sending by wireless news of the Allied front, he started for this enemy. Jack saw his friend's act, and, desiring to aid, turned his machine in the same direction.

But they had not gone far before they observed a number of black specks in the sky over the German lines.

"The Huns are coming," reflected Tom. "Now for some hot work."

And it came to him, to Jack, and the others, almost before they realized it. Tom never got a chance to attack the balloon he hoped to force to descend or to set on fire, for his attention was taken up by two German machines, which, separating from the others, headed straight for him. The lad gave one glance in the direction of Jack, and noted that a single Hun craft was about to engage with his chum.

"It's a regular German circus," thought Tom, referring to the number of hostile craft. "They delight to go out in numbers."

By this time the battle in the air had begun. It was a fight above the clouds, for both the French and the German machines were flying high, and had gone up above the bunches of fleecy vapor that now hid the ground from sight.

Tom headed straight for one of the Hun machines, seeking to get above it, always a point of vantage in an air battle, and as he rushed on he realized that his machine was being hit by bullets from one of the Hun guns.

Each bullet, as it struck, made a loud noise, as it punctured the tightly-drawn linen that covered the wings. But Tom knew that his craft could stand a number of such holes, if only the struts, the supports, and the guy wires were not broken. He had no time, now, to note what Jack or his comrades were doing, for his whole attention was taken up with the two Hun machines engaging him.

One seemed to be more skillful than the other, and to this one Tom gave his attention first. He emptied a stream of bullets full into this flier's craft, noting, after the first few bad shots, which he could tell by the tracers, that he had perfect range.

Guiding his craft with one hand and his feet, Tom worked the Lewis gun with his other hand, and he had emptied a whole drum at the daring Hun before he had the satisfaction of seeing the machine crumple up. Tom's bullets had struck some part that had caused the wings to collapse, and the airman went down to earth, his craft out of control.

But matters were not to go easy with the American. The other German was now in a better position for getting Tom than the latter was for potting him, and Tom felt a stream of bullets flying around him. One chipped his gun, and another grazed his cheek, the close call making his heart stand still for a moment. But he never faltered.

"I've got to get above him," Tom thought fiercely.

He made a risky spiral turn to one side, and began to mount, seeking to get in position to fire to better advantage. It was touch and go for a while, and he felt, rather than heard, his craft receive several bullets.

"If only the gasolene tank isn't hit," thought Tom.

But good fortune in this respect was with him, and he got in a position where he could point his machine (and the gun at the same time, for this is how the guns are aimed in the single aircraft) at the Hun flier. And then Tom sent forth a rain of bullets.

For a moment they seemed to have no effect, and yet Tom knew he had shot straight. Then, even while he felt a sharp pain in one hand, showing that he had been hit, he saw the other machine start down in a spinning nose dive. That meant he was going downward head first, and at the same time spinning around like a top.

This spinning nose dive may be intentional or accidental--that is, with the machine in control, or out of control. The spinning nose dive was discovered by accident, but is now part of the regular flying features, and is often used by aviators to escape from an enemy.

It is almost impossible to hit a plane doing a spinning nose dive, and if an aviator is over his own lines he may be able to come out of it before he reaches the ground, and so be safe. Many German planes have escaped in this way, and often a French airman has thought he has sent his enemy down disabled, when, as a matter of fact, the other has merely adopted this ruse to get away.

"Well, I don't know whether I got him, or whether he got frightened and went down to fool me," thought Tom. "Anyhow they're both out of the way, and I can go after the balloon."

But Tom could not, for two reasons. One was that the wound in his hand was bleeding profusely, and he knew it ought to be attended to before he was incapacitated. Another was that the balloon was being hauled down, and as more French planes were in the air now, making a number superior to the Huns, the latter turned tail and retreated.

It was inadvisable to follow them over their own lines now, and the squadron, or what was left of it, began to retreat. Tom noted the absence of three of the French planes, and among the missing was Jack's.

"I wonder if they got him," Tom mused, his heart becoming like lead. His eyes sought the air about him, but Jack's machine, which carried a little United States flag where it could easily be seen, was not in sight.

It was impossible to get any information up in the air. Tom would have to wait until they got back to the aerodrome. And he put on speed to get there the sooner, in order to end his suspense.

"And the other brave fellows--I wonder what happened to them," mused Tom. In his worry over the fate of Jack and the others he scarcely minded the pain in his hand.

He made a good landing, but being rather weak and faint from loss of blood, he scarcely heeded the congratulations of his comrades, who had received word, by telephone from the front, of the fate of some of the Hun machines. "Where's Jack?" Tom gasped, while a surgeon was putting a bandage on his hand.

"Right here, old scout!" came the unexpected answer, and Jack himself stepped out from amid a throng of airmen. "Why didn't you wait for me?" Jack went on. "I was coming back."

"Coming back? Did you come down safely?" asked Tom, beginning to feel a little better now. Then Tom realized the futility of his question, for was not Jack there in the flesh?

"Of course I came back, old scout," was the answer. "I had hard luck, though, but I'd have gone up again if they'd only waited for me."

"What happened?" asked Tom.

"Oh, just after I potted my man--or at least sent him down out of control--I got a bullet through my gasolene tank. Luckily it didn't set the petrol on fire, but I knew I'd better not take any chances. I tried to plug up the puncture with some chewing gum, but it wouldn't work. Guess the gum they sell now hasn't as much old rubber boot stock in it as it used to have. Anyhow it was leaking like a sieve, and I had to head for our lines."

"Tough luck!" consoled Tom. Jack did not add that he had, as soon as he landed, got into another machine, and was about to go back and join his comrades when they returned, having practically won the battle above the clouds.

Congratulations were extended to the members of the squadron, who accepted their honors modestly enough, as was characteristic of them.

Then, after Tom's wound had been dressed, and he and Jack were talking over the events of the day, there came a communication from the commander of the air division in that sector. It was an order calling on certain men to report at once for special duty. A picked squadron was to be detailed for a hazardous enterprise, it was said.

"And our names are there!" cried Jack. "Tom, old man, we're going!"

"But where is it?" asked another American flier named Boughton. "What's the game?"

Knowing the secret would be safe with him Tom said:

"We're going to pot the big German cannon that's bombarding Paris!"

Chapter XVI

Missing

News of the shelling of Paris by the long-range gun had, of course, been received at the aerodrome, though there had not, as yet, many details come in. Tom and Jack, as the latest arrivals from the big city, were called upon to tell all they knew, and they related their experiences in the raids, and also told about the various theories of the big gun.

"But how are we going to find it?" asked. Boughton. "It's easy enough, of course, for our squadron to go out with a lot of bombs. But where are we going to drop 'em?"

"Oh, we're to go to Paris for further instructions before starting on the quest," said Tom, who had made some inquiries about the orders concerning the picked squadron.

"And they may have discovered its location by this time," added Jack. "We know about where it is--somewhere in the sector between Hamegicourt and Conde. The rest ought to be easy."

"Not so easy as it sounds, my friends," put in a French flier. "I know that region. It is a big one; and the Germans no doubt have their gun well camouflaged. It will not be easy."

"But we'll get it!" asserted Tom.

"Naturally," said the Frenchman, as if that was all there was to it.

Tom's wound was painful, but not dangerous, though it would keep him on the ground for a day or two. Though, as a matter of fact, none of the members of the picked squadron was allowed to go aloft after the orders came detailing them for work in connection with the monster cannon. Their places were taken by others who were sent for, some being new fliers who were burning to make a name for themselves.

Besides Tom and Jack, in the picked squadron there were Boughton, another American, Cerfe and Tierse, two intrepid Frenchmen, and Haught, an Englishman, who insisted, but with little success, that his name be pronounced as though spelled "Hoo."

These six were to be depended on to find and destroy the German cannon--all of them if there were more than one, as was likely. And to this picked squadron other members would be added as need arose. All six were skillful fliers, and brave men of the air, as may easily be guessed. They were to use whatever type of machine they liked best--the single seaters, the great bombing planes, and, it was even said, one of the immense Italian fliers. This last was a craft capable of carrying several men and a quantity of supplies and ammunition.

Very soon, then, Tom Raymond and Jack Parmly were on their way to Paris again, accompanied by their comrades, and all would soon be engaged in the difficult and perilous task of finding the new German long-range cannon.

"I suppose you'll make another attempt to find your father?" suggested Jack to his chum, as they rode in on the train.

"Indeed I shall, if I have time. I can't understand why I haven't had some word before this. There are several possible reasons, of course. If it wasn't that we know he got to Rue Lafayette I'd say his ship had been sunk 'without a trace,' as the Germans ordered in other cases. But, of course, he safely reached this side. Then he just seems to have dropped out of sight, for I can't believe he was killed when the shell from the big gun hit the house where he had taken lodging. He may have found it advisable to return home at once, for some reason, and didn't have a chance to leave any word for me, or send me any message. And perhaps he hasn't got back to America yet. Then, too, he may be in Germany, a prisoner."

"Let us hope not," said Jack, softly, and Tom echoed the wish.

Much as he wished he could devote some time to the search for his father, Tom realized that he was working under military orders, and, however dear his father was to him, the sacrifice of his personal affairs must be made. He knew he would only have time to make some brief inquiries, and then he and Jack must go with the squadron to the headquarters assigned to it, as near the location of the big German gun as possible, and there try to silence it.

The train the picked squadron was traveling on was late, and it was dusk when they alighted at the railroad station.

"Think we'll have a chance to see anything of the bombardment?" asked Boughton.

"I was going to say I hoped not," answered Tom, "for I wish the beastly gun, or guns, would blow up. But that would take away our chance to pot 'em, and I know we all want to do that. You may see something, though they don't bombard at night as often as they do by day. Of late, however, before we left, the night firing was more frequent. Possibly they have found some means of hiding the gun flashes or of letting them mingle with others along a line so the exact location of the big Bertha is a matter of doubt."

As they alighted from the train, and were about to seek some taxicabs to take them to lodgings that had been assigned them, they all became aware of the fact that something unusual was going on. Suddenly the electric lights went out, leaving the region about the station, and indeed all of Paris, in comparative darkness.

At the same time a motor fire engine rushed screeching through the streets, giving an alarm.

"What is it?" cried Boughton. "Is the big gun firing?"

"It's a Zeppelin raid! I was here once before when they had one," said the Englishman coolly. "Mind your heads, boys. Just our rotten luck not to have a machine to go up after it."

He hurried out into the open street where he could have a view of the sky, and the others followed. There was more excitement than during the bombardment of the big gun. People were rushing here and there in search of safe places, and taxicabs, with their lamps like fireflies in the darkness, were skidding hither and yon, their horns calling for a clear way.

Suddenly there was a muffled roar, at some distance off. This was followed by a hoarse murmur, as though a burst of rage from many throats at the unspeakable outrage of the Huns in killing women and children.

At the same time the anti-aircraft guns, with which Paris is so efficiently guarded, began to bark and to send their red flashes out into the blackness of the night. They were shooting at the Zeppelin, as yet unseen by the men of the picked squadron, and the gunners aimed according to instructions sent them by wireless from scouts hovering in the air above the city.

As soon as word comes from the front, about eighty miles from Paris, that a Zeppelin is on its way to raid, an elaborate system of defense is put into operation. There are some airmen above Paris all the while, frequently as many as forty on sentry duty. But when word comes of a Zeppelin raid the whole squadron, numbering close to three hundred, goes aloft. By their searchlights, aided by those on the surface, these fliers endeavor to pick up the German machine, and, too, they endeavor to get near enough to attack it.

This was what was now going on. Pandemonium appeared let loose, and the explosion of the German bombs, mingling with the noise of the French guns, made Paris seem like a battlefield. Occasionally could be heard, when the guns were silenced for a moment, the roar of the many aeroplane motors aloft.

The Zeppelin seemed to be over a section of Paris near the Tuileries, judging by the bursts of light in that direction. Tom, Jack, and their friends wished with all their hearts that they might take a hand in the defense, but it was not to be. For perhaps half an hour the anti-aircraft guns roared out their defiance to the Hun, and then a large flare of gasolene was lighted in a public square.

This was a signal for the aeroplanes to return, for the Zeppelin had left, either because she found the situation too perilous for her, or because she had used up all her bombs.

The lights were turned on again, and the new arrivals watched the aeroplanes returning one by one, being recognized by their lights in the air as they moved about like gigantic illuminated insects.

"Well, that's some excitement," observed Tom, as he and the oth