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TOM SWIFT AND HIS AERIAL WARSHIP

or The Naval Terror of the Seas

BY VICTOR APPLETON

CHAPTER I

"What's the matter, Tom? You look rather blue!"

"Whew!"

Ranged on the sides of the room were models of many queer craft, most of them flying machines of one sort or another, while through the open door that led into a large shed could be seen the outlines of a speedy monoplane.

"Bless my gasoline tank!" exclaimed Tom, with a laugh, in imitation of the gentleman Ned Newton had mentioned, "I know that! I'm not worrying over the loss of any friends."

"That's enough!" exclaimed Tom. "It isn't that, I tell you."

"Quite a combination of colors," admitted Tom. "But it isn't what you think. It's just that I'm puzzled, Ned."

"Yes, genuinely puzzled."

"No, not exactly that, though it is about one of my inventions I am puzzled. I guess I haven't shown you my very latest; have I, Ned?"

"Well, this isn't so very new," went on the young inventor, for Tom Swift had designed and patented many new machines of the air, earth and water. "I'm just trying to work out some new problems in aerial navigation, Ned," he went on.

"Come, now, none of that!" exclaimed Tom, with a laugh. "Why, the surface of aerial navigation has only been scratched. The science is far from being understood, or even made safe, not to say perfected, as water and land travel have been. There's lots of chance yet."

Through the open windows came the hum of distant machinery, for Tom Swift and his father were the heads of a company founded to manufacture and market their many inventions, and about their home were grouped several buildings. From a small plant the business had grown to be a great tree, under the direction of Tom and his father.

"And, Ned," he went on, "there's no reason why you shouldn't see it. I've been keeping it a bit secret, until I had it a little further advanced, but I've got to a point now where I'm stuck, and perhaps it will do me good to talk to someone about it."

"Well, perhaps you can, just the same, though you may not know a lot of technical things about machines. It sometimes helps me just to tell my troubles to a disinterested person, and hear him ask questions. I've got dad half distracted trying to solve the problem, so I've had to let up on him for a while. Come on out and see what you make of it."

"Oh, it isn't anything like that," Tom answered with a laugh. "I might as well give you a few hints, so you'll know what I'm driving at. Then I'll take you out and show it to you."

"This happens to be air."

"Something like that. I call it my aerial warship, though."

"It will be dangerous, too, if I can get it to work. That's what it's intended for."

"Yes, I know," interrupted Tom, "and I appreciate all that when I called my newest craft an aerial warship."

"Oh, mine is large enough," Tom broke in.

"Well, not exactly," Tom said. "But what I was going to tell you was that all guns are not necessarily large. You can get big results with small guns and projectiles now, for high-powered explosives come in small packages. So it isn't altogether a question of carrying a certain amount of weight. Of course, an aerial warship will have to be big, for it will have to carry extra machinery to give it extra speed, and it will have to carry a certain armament, and a large crew will be needed. So, as I said, it will need to be large. But that problem isn't worrying me."

"It's the recoil," said Tom, with a gesture of despair.

"Yes, from the guns, you know. I haven't been able to overcome that, and, until I do, I'm afraid my latest invention will be a failure."

"I'm afraid I can't help you any," he said. "The only thing I know about recoils is connected with an old shotgun my father used to own.

"Well, I fired the gun. But it must have had a double charge in it and been rusted at that. All I know is that after I pulled the trigger I thought the end of the world had come. I heard a clap of thunder, and then I went flying over backward into a blackberry patch."

"The what?" asked Ned.

"Oh, yes," observed Ned, rubbing his shoulder in a reflective sort of way. "I always thought it was something like that. But, at the time I put it down to an explosion, and let it go at that."

"This went mostly backward--in my direction," said Ned ruefully.

"Is that what makes you look so blue?" asked Ned.

"Then you haven't actually tried it out yet?" asked Ned.

"I suppose not," agreed Ned. "And is it only the recoil that is bothering you?"

The two chums crossed the yard, threading their way through the various buildings, until they stood in front of the structure to which Tom had called attention.

Ned was a little startled at the look on Tom s face and the sound of alarm in his chum's voice.

CHAPTER II

"Something wrong?" asked the young bank clerk.

"Oh, it's you, is it, Koku?" he asked, as a veritable giant of a man came forward.

"Oh, is my father here?" asked Tom. "I was wondering who had opened the door of this shed."

"That's all right, Dad. Ned and I came out to wrestle with that recoil problem again. I want to try some guns on the craft soon, but--"

"I never will. I'll make it work, Dad!"

"Well, Dad, we'll see," began Tom easily. "There she is, Ned," he went on. "Now, if you'll come around here

"Bless my socks, Tom!" cried the short, stout man. "There sure is trouble!"

"What's the matter?" interrupted Tom, jumping forward. "Speak out! Eradicate! Mr. Damon, what is it?"

"It's on fire!" yelled the colored man.

Instantly the place was in confusion. Tom and Ned, looking from a window of the hangar, saw a billow of black smoke roll across the yard. But already the private fire bell was clanging out its warning. And, while the work of fighting the flames is under way, I will halt the progress of this story long enough to give my new readers a little idea of who Tom Swift is, so they may read this book more intelligently. Those of you who have perused the previous volumes may skip this part.

Mr. Swift was a widower, and lived with Tom, his only son, in the village of Shopton, New York State. Mrs. Baggert kept house for them, and an aged colored man, Eradicate Sampson, with his mule, Boomerang, did "odd jobs" about the Shopton home and factories.

Tom took Koku into his service, somewhat to the dismay of Eradicate, who was desperately jealous. But poor Eradicate was getting old, and could not do as much as he thought he could. So, in a great measure, Koku replaced him, and Tom found much use for the giant's strength.

From then on Tom had passed a busy life, making many machines and having some thrilling times with them. Just previous to the opening of this story Tom had made a peculiar instrument, described in the volume entitled "Tom Swift and His PhotoTelephone." With that a person talking could not only see the features of the person with whom he was conversing, but, by means of a selenium plate and a sort of camera, a permanent picture could be taken of the person at either end of the wire.

But just at present other matters than the warship were in Tom's mind. The red shed was on fire.

"The red shed!" Tom cried. "We mustn't let that get the best of us! Everybody at work! Father, not you, though. You mustn't excite yourself!"

"But, Tom, I can help," objected the aged inventor.

"But, Tom, it--it's the red shed!" gasped Mr. Swift.

"Yes, Master," replied the giant, in correct but stilted English. "I have set the indicator to signal the alarm in every shop on the premises."

"Yais, sah! Heah I is!" answered the colored man. "I'll go git mah mule, Boomerang, right away, an' he--"

"Now dat's so, Massa Tom. But I could put blinkers on him, an'--"

"Yes, Tom, I'm right here," answered the peculiar man, for he had come over from his home in Waterford to pay a visit to his friends, Tom and Mr. Swift. "I'll do anything I can to help you, Tom, bless my necktie!" he went on. "Only say the word!"

Those in the shed where was housed what Tom hoped would prove to be a successful aerial warship rushed to the open. From the other shops and buildings nearby were pouring men and boys, for the Swift plant employed a number of hands now.

"My, you've got a big enough fire-fighting force, Tom!" cried Ned in his chum's ear.

Tom pointed to where a shed, painted red--a sign of danger-could be seen partly enveloped in smoke, amid the black clouds of which shot out red tongues of flame.

"Because--" Tom began, but the rest of the sentence was lost in a yell.

"Don't take that!" Tom cried. "Don't use that hose! Drop it!"

"No, but if they pull it out the water will be turned on automatically."

"Not at this fire," was Tom's answer. "There's a lot of calcium carbide in that red shed--that's why it's red--to warn the men of danger. You know what happens when water gets on carbide--there's an explosion, and there's enough carbide in that shed to send the whole works sky high.

CHAPTER III

Tom's tones and voice were so insistent that the giant and the colored man had no choice but to obey. They dropped the hose which, half unreeled, lay like some twisted snake in the grass. Had it been pulled out all the way the water would have spurted from the nozzle, for it was of the automatic variety, with which Tom had equipped all his plant.

"I don't know--yet, but I know water is the worst thing you can put on carbide," returned Tom. For all he spoke Slowly his brain was working fast. Already, even now, he was planning how best to give battle to the flames.

Yet the fire needed to be coped with. Already the flames were coming through the roof, and the windows and door were spouting red fire and volumes of smoke.

"Ha! Massa Tom say drop de hose, but how yo' gwine t' squirt watah on a fire wifout a hose; answer me dat?" and Eradicate looked at Koku.

"Huh! Maybe yo' could do dat in cannibal land, where yo' all come from," spoke Eradicate, "but yo' can't do dat heah! 'Sides, de red shed will blow up soon. Dere's suffin' else in dere except carbide, an' dat's gwine t' go up soon, dat's suah!"

"Dat's what I wanted t' do, but Massa Tom say I cain't," explained the colored man. "Golly! Look at dat fire!"

"Tom, you must do something," said Mr. Swift. "If the flames once reach that helmanite--"

"But something will have to be done!" exclaimed Mr. Damon. "Bless my red necktie, if we don't--"

His words of warning had their effect, and the whole circle moved back several paces.

"I should say there was!" Tom answered. "I hoped we could get some of them out, but we can't now--until the fire dies down a bit, at any rate."

"It's from sparks!" Tom said.

"No, use all you like! That's the only thing to do. Come on, you with the hose!" Tom yelled. "Save the other buildings!"

"Yes, Father, I know. And I'm going to fight that fire in a new way. But we must save the other buildings, too. Play water on all the other sheds and structures!" ordered the young inventor. "I'll tackle this one myself. Oh, Ned!" he called.

"You take charge of protecting the place where the new aerial warship is stored. Will you? I can't afford to lose that."

"Not if you don't use too much. Some of the woodwork isn't varnished yet, and I wouldn't want it to be wet. But do the best you can. Take Koku and Eradicate with you. They can't do any good here."

"Not a bit of it, Ned. But I have another plan I want to try. Lively now! The wind's changing, and it's blowing over toward my aerial warship shed. If that catches--"

"I wonder what Tom is going to do?" mused Ned, as he neared the big shed he and the others had left on the alarm of fire.

"The dirigible shed! I wonder what his game is? Surely that can't be in danger--it's too far off!"

Meanwhile several members of the fire-fighting force that had been summoned from the various shops by the alarm, had made an effort to save from the red shed some of the more valuable of the contents. There were some machines in there, as well as explosives and chemicals, in addition to the store of carbide.

"Keep away!" warned Mr. Swift. "It will explode soon. Keep back!"

Warned by the aged inventor, the throng of men began slowly moving away from the immediate neighborhood of the blazing shed. Though it may seem to the reader that some time has elapsed since the first sounding of the alarm, all that I have set down took place in a very short period--hardly three minutes elapsing since Tom and the others came rushing out of the aerial warship building.

The young bank clerk saw a strange sight. From the top of the dirigible balloon shed a long, black, cigar-shaped body arose, floating gradually upward. The very roof of the shed slid back out of the way, as Tom pressed the operating lever, and the dirigible was free to rise--as free as though it had been in an open field.

Ned did not finish his half-formed sentence. A dreadful thought came into his mind. What if the sudden fire, and the threatened danger, as well as the prospective loss that confronted Tom, had affected his mind?

"What can he be up to?" marveled Tom. "Is he going to run away from the fire?"

Then, as they watched, Ned and the others saw the direction of the balloon change. She turned around in response to the influence of the rudders and propellers, and was headed straight for the blazing shed, but some distance above it.

He did not have long to wait to find out.

"He can't be dousing water on from up above there," reasoned Ned. "Pouring water on carbide from a height is just as bad as spurting it on from a hose, though perhaps not so dangerous to the persons doing it. But it can't be--"

"Fine for you. Tom Swift! Fine!"

CHAPTER IV

"Tom's done the trick!" yelled Ned, paying little attention now to the big airship shed, since he saw that the danger was about over.

"Huh! Your mule afraid of fire," remarked Koku.

"That'll do, Rad!" broke in Ned, with a laugh. He knew that when Tom's helper grew excited on the subject of his mule there was no Stopping him, and Boomerang was a point on which Eradicate and Koku were always arguing. "The fire is under control now."

"Visiting?" queried Ned, in some surprise.

"Oh, I understand!" laughed Ned. "Yes, and I hope it doesn't pay us another visit soon. Oh, look at Tom, would you!" he cried, for the young aviator had swung his ship about over the flames, to bring another row of sand bags directly above a place where the fire was hottest.

Moving slowly, the airship hovered over every part of the now slowly expiring flames, the burned opening in the roof of the shed making it possible for the sand to reach the spots where it was most needed. The flames died out in section after section, until no more could be seen--only clouds of black smoke.

"Almost out," answered Mr. Damon. "A little more sand, Tom."

"Haven't much more sand left," was Tom's comment, as he sent down a last shower. "That will have to do. Hustle that carbide and other explosive stuff out of there now, while you have a chance."

"Me like work," answered the giant, stretching out his great arms.

As all the sand ballast had been allowed to run out Tom was obliged to open the gas-valves and let some of the lifting vapor escape, or he could not have descended.

"Bless my insurance policy, yes," exclaimed Mr. Damon. "That was a fine move of yours."

"But I didn't know where to get any until I happened to think of the ballast bags of my dirigible. Then I knew, if I could get above the fire, I could do the trick. I had to fly pretty high, though, as the fire was hot, and I was afraid it might explode the gas bag and wreck me."

"Oh, well, you have to take chances in this business," observed Tom, with a smile. "Now, then, let's finish this work."

"I wish I could help you, Tom," said his aged father. "I don't seem able to do anything but stand here and look on," and he gazed about him rather sadly.

"Yes, of course!" exclaimed the odd man, catching a wink from Tom, who wanted his father not to get too excited on account of his weak heart. "Come along, Professor Swift. The danger is all over."

"And, Dad, when you haven't anything else to do," went on Tom, rather whimsically, "you might be thinking up some plan to take up the recoil of those guns on my aerial warship. I confess I'm clean stumped on that point."

"Don't you believe it, Dad!" cried Tom, with more of a jolly air of one chum toward another than as though the talk was between father and son. "You solve the recoil problem for me, and I'll take care of the rest, and make the air warship sail. But we've got something else to do just now. Lively, boys."

Soon large openings were made on three sides of the red shed, or rather, what was left of it, and through these the dangerous chemicals and carbide, in sheet-iron cans, were carried out to a place of safety. In a little while nothing remained but a heap of hot sand, some charred embers and certain material that had been burned.

"Well, yes, there's more lost than I like to think of," answered Tom slowly, "but it would have been a heap sight worse if the stuff had gone up. Still, I can replace what I've lost, except a few models I kept in this place. I really oughtn't to have stored them here, but since I've been working on my new aerial warship I have sort of let other matters slide. I intended to make the red shed nothing but a storehouse for explosive chemicals, but I still had some of my plans and models in it when it caught."

"Yes. It's lucky I had plenty of ballast aboard the dirigible. You see, I've been running it alone lately, and I had to take on plenty of sand to make up for the weight of the several passengers I usually carry. So I had plenty of stuff to shower down on the fire. I wonder how it started, anyhow? I must investigate this."

"Yes. At least they gave the alarm. Guess I'll ask Eradicate how he happened to notice. Oh, I say, Rad!" Tom called to the colored man.

"How'd you happen to see the red shed ablaze?" Tom asked.

"Oh, never mind the carrot, or Boomerang, either, Rad!" broke in Tom, "I'm asking you about the fire."

"Yes, I heard you yell," Tom said. "But what I wanted to know is, did you see anyone near the red shed at the time?"

"I wonder if Mr. Damon did? I must ask him," went on the young inventor. "Come, on, Ned, we'll go up to the house. Everything is all right here, I think. Whew! But that was some excitement. And I didn't show you my aerial warship after all! Nor have you settled that recoil problem for me."

"That's right. Well, Koku, what is it?" for the giant had approached, holding out something in his hand.

"Oh, you think it's something explosive, eh?" asked Tom, as he took the object from the giant.

Tom did not speak for a moment. Then he cried:

CHAPTER V

What Tom Swift held in his hand looked like a small cannon ball, but it could not have been solid or the young aviator would not so easily have held it out at arm's length for his friend Ned Newton to look at.

"Is that likely to go off?" the bank clerk asked, as he came to a halt a little distance from his friend.

"Damage? It looks to me as though it had suffered the most damage itself. What is it, one of your models? Looks like a bomb to me."

"Not one of those you're going to use on your aerial warship, is it, Tom?"

"Do you really mean it?" cried Ned.

"Well, if that's the case, I wouldn't leave such dangerous things around where there are explosives, Tom."

"If it had worked at night, when we were all asleep, we might not have put the fire out so easily. This sure is suspicious! I'm glad you found this, Koku."

What he saw was merely a hollow shell of iron, with a small opening in it, as though intended for a place through which to put a charge of explosives and a fuse.

"I know it," said Tom quietly. "It wasn't an explosive bomb. Smell that!"

"Oh, don't get nervous," laughed Tom. "It can't hurt you now. But what does that smell like?"

"Why," he said slowly, "I don't just know the name of it, but it's that funny stuff you mix up sometimes to put in the oxygen tanks when we go up in the rarefied atmosphere in the balloon or airship."

"Do you really think that, Tom?" cried Ned.

"Why--why--that would mean some one tried to set fire to the red shed, Tom!"

"You mean some one purposely put that bomb in the red shed, Tom?"

"He knew the fire would be practically unquenchable by ordinary means, and he counted on its soon eating its way into the carbide and other explosives. Only it didn't."

"Exactly," Tom said, "only this was more delicate, and, if it had worked properly, there wouldn't have been a vestige left to give us a clue. But the fire, thanks to the ballast sand in the dirigible, was put out in time. The fuse burned itself out, but I can tell by the smell that chemicals were in it. That's all, Koku," he went on to the giant who had stood waiting, not understanding all the talk between Tom and Ned. "I'll take care of this now."

"Well, yes, I guess you could say it was a bad man," replied Tom.

"I wouldn't like to be that man, if Koku catches him," observed Ned. "Have you any idea who it could be, Tom?"

"It wouldn't be Andy Foger, would it?"

"How about those diamond-makers, whose secret you discovered? They wouldn't be trying to get back at you, would they?"

"What are you going to do about it?" Ned asked.

"You mean trying to find out who these fellows are?"

"Well, I guess I am!" cried the bank clerk with sparkling eyes. "I wouldn't ask anything better. We've been in things like this before, Tom, and we'll go in again--and win! I'll help you all I can. Now, let's see if we can pick up any other clues. This is like old times!" and Ned laughed, for he, like Tom, enjoyed a good "fight," and one in which the odds were against them.

"Then you're not going to give up your aerial warship idea?"

"Well, the way your father spoke--"

"Then you are going to make a go of it?"

Tom paused, on his way to the house, to put the bomb in one of his offices.

"That's right," agreed Ned.

The young inventor, finding his father quieted down and conversing easily with Mr. Damon, who was blessing everything he could think of, motioned to Ned to follow him out of the house again.

But, it must be confessed, after Tom and Ned had spent the rest of that day in and about the burned shed, they were little wiser than when they started. They found the place where the fire bomb had evidently been placed, right inside the main entrance to the shed. Tom knew it had been there because there were peculiar marks on the charred wood, and a certain queer smell of chemicals that confirmed his belief.

"A lucky provision," observed Ned.

Close questioning of the workmen failed to disclose anything. Tom was particularly anxious to discover if any mysterious strangers had been seen about the works. There was a strict rule about admitting them to the plant, however, and it could not be learned that this had been violated.

"I'm ready, if you are," Ned agreed, "though I know about as much of those things as a snake does about dancing. But I'm game."

"I wonder what he has on his mind," remarked Ned musingly.

As they neared the colored man, they could hear him saying:

"What's that, Eradicate?" asked Tom.

"A man--what sort of a man?" asked Tom, always ready to be suspicious of anything unusual.

"He does, eh?" cried Tom. "What sort of a man was he, Rad?"

"Ned, there may be something in this!" said Tom, in an excited whisper to his chum. "I don't like the idea of a mysterious stranger questioning Eradicate!"

CHAPTER VI

"Rad, just exactly what sort of a man was this one you speak of?" asked Tom.

"Yes, I know that much. You've said it before. But was he an Englishman, an American--or--"

"I think he were a Frenchman," spoke Eradicate. "I done didn't see him eat no frogs' laigs, but he smoked a cigarette dat had a funny smell, and he suah was monstrous polite. He suah was a Frenchman. I think."

"Tell us more about him, Rad," he suggested. "Did he seem especially interested in the fire?"

"But every once in a while he put in some question about the fire, or about our shops, didn't he, Rad?" Tom wanted to know.

"How yo' all done guess dat?" he asked.

"Yes, sah, he done did ask about yo', and de wuks, ebery now and den," Rad confessed. "But how yo' all knowed dat, Massa Tom, when I were a-tellin' yo' all about him astin' fo' mah mule, done gets me--dat's what it suah does."

Eradicate looked reproachfully at his master.

"Yes, I know I gave those orders," Tom said, with a smile, "but I want to make sure that they have been followed."

"Then you didn't tell this queer stranger, Frenchman, or whatever he is, much about my place?"

Ned uttered an exclamation of surprise.

"Dat's what I means," the colored man went on. "I done fooled him. When he asted me about de fire I said it didn't do no damage at all--in fack dat we'd rather hab de fire dan not hab it, 'case it done gib us a chance t' practice our hose drill."

"Well, he done sort ob hinted t' me ef we all knowed how de fire done start. I says as how we did, dat we done start it ourse'ves fo' practice, an dat we done expected it all along, an' were ready fo' it. Course I knows dat were a sort of fairy story, Massa Tom, but den dat cigarette-smokin' Frenchman didn't hab no right t' asted me so many questions, did he?"

"T' see ef I wants t' sell mah mule, Boomerang, yais, sah. I sort ob thought maybe you'd want t' hab a look at dat man, so I tole him t' come on. Course I doan't want t' sell Boomerang, but ef he was t' offer me a big lot ob money fo' him I'd take it."

"I won't, Massa Tom," promised the colored man, as he went off muttering to himself.

"I don't know just what to think, Ned. Of course things like this have happened before--persons trying to worm secrets out of Eradicate, or some of the other men."

"But about this Frenchman?"

"Do you think he'll come to bargain with Eradicate about the mule?" Ned asked.

"And you were right."

"That's great, Tom! But do you think this fellow had anything to do with the fire?"

"It's too bad!" declared Ned. "Seems as though they might let you alone, if they haven't gumption enough to invent things for themselves."

The young inventor unlocked the door of the shed where he kept his latest "pet," and at the sight which met his eyes Ned Newton uttered an exclamation of surprise.

"My aerial warship!" was the quiet answer.

"Tom, however did you do it?" gasped Ned at length.

In brief Tom's aerial warship was a sort of German Zeppelin type of dirigible balloon, rising in the air by means of a gas container, or, rather, several of them, for the section for holding the lifting gas element was divided by bulkheads.

This is not so with a dirigible balloon. It is held in the air by means of the lifting gas, and once so in the air can be sent in any direction by means of propellers and rudders.

Sufficient to say that Tom's craft consisted first of a great semi-rigid bag, or envelope, made of specially prepared oiled silk and aluminum, to hold the gas, which was manufactured on board. There were a number of gas-tight compartments, so that if one, or even if a number of them burst, or were shot by an enemy, the craft would still remain afloat.

But this was not all.

"They look just like places where you intend to mount guns," said Ned to Tom.

"Then you intend to fight with this ship?" asked Ned.

"What do you mean?"

"Then you're going to do the same with this aerial warship as you did with your big lantern and that immense gun you perfected?" asked Ned.

"When do you expect the government experts?," Ned asked.

"Fire away," laughed Ned. "I'll do the best I can."

"There you are, Tom!" he cried. "Why not take up the recoil of the guns on your aerial warship by some such device as that?" and Ned pointed to the door-check.

CHAPTER VII

"Wouldn't that do, Tom? Check the recoil of the gun with whatever stuff is in that arrangement!"

"By Jove, Ned, old man!" he cried. "I believe you've struck it! And to think that has been under my nose, or, rather, over my head, all this while, and I never thought of it. Hurray! That will solve the problem!"

"I'm almost sure it will. I'll give it a trial right away."

"They are a combination of springs and hydrostatic valves," began Tom.

"A valve through which liquids pass. In this door-check there may be a mixture of water, alcohol and glycerine, the alcohol to prevent freezing in cold weather, and the glycerine to give body to the mixture so it will not flow through the valves too freely."

"I think so," spoke Tom. "I'm going to work on it right away, and we'll soon see how it will turn out It's mighty lucky you thought of that, for I sure was up against it, as the boys say."

"If the thing works I'll give you due credit for it," promised Tom. "Now, I've got to figure out how much force a modified hydrostatic valve check like that will take up, and how much recoil my biggest gun will have."

"Yes, four quick-firers, at least, two on each side, and heavier guns at the bow and stern, to throw explosive shells in a horizontal or upward direction. For a downward direction we won't need any guns, we can simply drop the bombs, or shells, from a release clutch."

"Well, if it's necessary, yes. Though I guess there won't be much chance of doing that to a rival aeroplane or dirigible. But in flying over cities or forts, explosive bombs can be dropped very nicely. For use in attacking other air craft I am going to depend on my lateral fire, from the guns mounted on either beam, and in the bow and stern."

"No, I don't believe I'll go that far," Tom replied. "Though, if the government wants my craft, I may have to go aloft and fire shots at targets for them to show them how things work.

"I suppose that's right," agreed Ned. "Have you any of your guns ready?"

There was considerable detailed figuring and computation work ahead of Tom Swift, and I will not weary you by going into the details of higher mathematics. Even Ned lost interest after the start of the problem, though he was interested when Tom took down the door-check and began measuring the amount of force it would take up, computing it on scales and spring balances.

"And now to see how much recoil force my guns develop!"

"Surely," answered Tom. "That's the only way to get at real results. I'll have the guns taken out and mounted in a big field. Then we'll fire them, and measure the recoil."

This was the second or third day after the fire in the red shed, and in the interim Tom had been busy making computations. These were about finished. Meanwhile further investigation bad been made of clues leading to the origin of the blaze in the shed, but nothing had been learned.

Ned was much interested in the guns, and, a little later, he helped Tom and Koku mount them in a vacant lot. The giant's strength came in handy in handling the big parts.

"It will never work, Tom, never!" declared the aged inventor, when informed. "You can't take up those guns in your air craft, and fire them with any degree of safety."

Ned smiled with pleasure at this.

"When are they coming?" asked Ned, as he and Tom went out one morning to make the first test of the guns.

"Me no drop any, Master," spoke the giant, as he lifted the boxes of explosives in his strong arms.

"Here, Rad, where are you going?" Tom asked, as he noticed the colored man walking away, after having completed a task assigned to him.

"Yes, Rad, that's what I asked you."

"Nonsense! It isn't anywhere near noon yet."

"Oh, well, trot along," laughed the young inventor. "I guess we won't need you. Is everything all right there, Koku?"

"Now, Ned, if you'll stand here," went on Tom, "and note the extreme point to which the hand on the pressure gauge goes, I'll be obliged to you. Just jot it down on this pad."

"It's Mr. Damon," observed Tom. "We'll wait until he arrives. He'll be interested in this."

"Just practicing," replied the young inventor. "Getting ready to put the armament on my aerial warship."

"Perfectly," Tom replied. "Now then, Ned, I think we'll fire."

"Catch the figure, Ned!" Tom cried.

"Good! And I can build a recoil check that will take up to one hundred and twenty thousand pounds pressure. That ought to be margin of safety enough. Now we'll try another shot."

"But I can easily put a larger hydrostatic check on them," he said. "Now, we'll fire by batteries, and see what the total is."

The young inventor was busy making some calculations after the last of the firing had been completed. Koku was packing up the unfired shells, and Mr. Damon was blessing his ear-drums, and the pieces of cotton he had stuffed in to protect them, when a tall, erect man was observed strolling over the fields in the direction of the guns.

"Yes, and a stranger, too," observed Tom. "I wonder if that can be Eradicate's Frenchman?"

"I beg your pardon," he began, addressing everyone in general, "but I am looking for Tom Swift. I was told he was here."

"Ah! Well, I am Lieutenant Marbury, with whom you had some correspondence recently about--"

"That is it--yes. Have you it ready for a trial flight?"

"A fire!" exclaimed the officer in surprise. "How was that? We heard nothing of it in Washington."

"Ha!" exclaimed Lieutenant Marbury. "This fits in with what I have heard. And did you not receive warning?" he asked Tom.

"Of foreign spies!" was the unexpected answer. "I am sorry. Some of our Secret Service men unearthed something of a plot against you, and I presumed you had been told to watch out. If you had, the fire might not have occurred. There must have been some error in Washington. But let me tell you now, Tom Swift--be on your guard!"

CHAPTER VIII

"Do you really mean that?" asked the young inventor, looking around to make sure his father was not present. On account of Professor Swift's weak heart, Tom wished to spare him all possible worry.

"And that was--what?" asked Tom.

"And why have they singled me out?" Tom demanded.

"Well, now, I won't be so sure," Tom confessed. "I have been working very hard, the last two days, making some intricate calculations. I have rather neglected my mail, to tell you the truth.

"Ha! That was it!" cried the lieutenant. "It was the warning in cipher or code. I didn't think they would neglect to send it to you."

"You must also have received a method of deciphering the message," the officer said. "Probably you overlooked that. The Secret Service men sent you the warning in code, so it would not be found out by the plotters, and, to make sure you could understand it, a method of translating the cipher was sent in a separate envelope. It is too bad you missed it."

"Owing to the fact that Tom put the fire out with sand ballast from his dirigible!" cried Ned. "You should have seen it!"

"I shall," Tom decided. "But, if we want to talk, we had better go to my office, where we can be more private. I don't want the workmen to hear too much."

"Did you come on from Washington yesterday?" asked Tom, as he, Ned and the officer strolled toward the shed where was housed the aerial warship.

"Glad you did," Tom said. "I'll soon have something to show you, I hope. But I am interested in hearing the details of this suspected plot. Are you sure one exists?"

"We are convinced in Washington," went on Lieutenant Marbury, when he, Tom and Ned were seated in the private office, "that foreign spies are at work against you and against our government."

"Because of the inventions you have perfected and turned over to Uncle Sam--notably the giant cannon, which rivals anything foreign European powers have, and the great searchlight, which proved so effective against the border smugglers. The success of those two alone, to say nothing of your submarine, has not only made foreign nations jealous, but they fear you--and us," the officer went on.

"But they won't!" interrupted the officer--"They are seeking to destroy those inventions. More than once, of late, we have nipped a plot just in time."

"They have. And now this fire proves that they are taking other measures--they are working directly against you."

"Either to prevent you from making further inventions, or to stop you from completing your latest--the aerial warship."

"Few secrets are safe from foreign Spies," declared Lieutenant Marbury. "They have a great ferreting-out system on the other side. We are just beginning to appreciate it. But our own men have not been idle."

"Are the French in it?" asked Ned impulsively.

"Tell him about Eradicate, and the man who wanted to buy the mule, Tom," suggested Ned,

"I think you are right," said Lieutenant Marbury. "And, as regards the French, I might say they are not the only nation banded to obtain our secrets--yours and the government's!"

"So they are, in a certain measure," the officer went on. "And Russia is, too. But, in all foreign countries there are two parties, the war party, as it might be called, and the peace element.

"And you think spies set this fire?"

"But what measures shall I adopt against this plot?" Tom asked.

A sudden knock on the door interrupted the speaker.

CHAPTER IX

"I don't know," Tom answered. "I left orders we weren't to be disturbed unless it was something important."

"It isn't a fire," Tom answered. "The automatic alarm would be ringing before this in that case."

"Well, what is it?" asked Tom a bit sharply.

"Oh, so I did," Tom exclaimed. "I had forgotten about that," he went on to Lieutenant Marbury and Ned. "I am in need of helpers to rush through the finishing touches on my aerial warship, and I left word, if any applied, as they often do, coming here from other cities, that I wanted to see them. How many are there?" Tom asked of the messenger.

"That's what they all say," interposed Tom, with a smile. "But, though they may be good mechanics in their own line, they need to have special qualifications to work on airships. Tell them to wait, Rodney," Tom went on to the lad, "and I'll see them presently."

"You were about to give me another warning when that interruption came. You might complete it now."

"Do you mean he is in danger?" asked Ned quickly.

Tom did not seem as alarmed as he might reasonably have been under the circumstances.

"That's just where I can't warn you," the officer replied. "I can only give you that hint, and beg of you to be careful."

"No, indeed; it isn't that!" the lieutenant hastened to assure the young man. "I would gladly tell, if I knew. But this plot, like the other one, directed against the inventions themselves, is so shrouded in mystery that I cannot get to the bottom of it.

"So we can only warn you to be careful, and this I do in all earnestness. That was part of my errand in coming here, though, of course, I am anxious to inspect the new aerial warship you have constructed. So watch out for two things--your inventions, and, more than all, your life!"

"I certainly do. These foreign spies are desperate. If they cannot secure the use of these inventions to their own country, they are determined not to let this country have the benefit of them."

"That's right!" agreed Ned. "And, if there's anything I can do, Tom, don't hesitate to call on me."

"I certainly would," was the ready answer. "But hadn't you better see those men who are waiting to find out about positions here?"

Followed by Ned and Lieutenant Marbury, Tom led the way into the big airship shed. There, Swaying about at its moorings, was the immense aerial warship. To Ned's eyes it looked complete enough, but, when Tom pointed out the various parts, and explained to the government officer how it was going to work, Ned understood that considerable yet remained to be done on it.

"It certainly is most complete," the officer observed. "And when you get the guns mounted I shall be glad to make an official test. You understand," he went on, to Tom, "that we are vitally interested in the guns, since we now have many aircraft that can be used purely for scouting purposes. What we want is something for offense, a veritable naval terror of the seas."

"Is that so?" asked the lieutenant, as Tom clapped his chum on the back.

"Oh, it isn't anything of the sort," Ned objected. "I just--"

"A good idea!" commented Lieutenant Marbury.

And, while this was being done by the pilot or captain in charge, the crew could be manning the guns with which hostile airships would be attacked, and bombs dropped on the forts or battleships of the enemy.

"Which ought to be in about a week," Tom said. "Meanwhile I shall be glad if you will be my guest here."

Leaving Ned and the lieutenant to entertain each other, Tom went to see the mechanics who had applied for places. He found them satisfactory and engaged them. One of them had worked for him before. The other was a stranger, but he had been employed in a large aeroplane factory, and brought good recommendations.

But finally one of the big guns, and two of the smaller ones were in place, with the apparatus designed to reduce the recoil shock, and then Tom decided to have a test of the Mars.

"Well, a little way up in the air, at least," Tom answered. "I'll make a sort of captive balloon of my craft, and see how she behaves. I don't want to take too many chances with that new recoil check, though it seems to work perfectly in theory."

The sun glistened on the bright brass and nickel parts, and glinted from the gleaming barrels of the quick-firing guns.

Tom, Ned, Lieutenant Marbury and Mr. Damon were aboard the captive Mars.

The recoil apparatus was in place, and it now remained to see if it would do the work for which it was designed.

"Bless my accident insurance policy!" exclaimed Mr. Damon. "I'm as ready as ever I shall be, Tom. Let 'em go!"

"Here we go!" cried the young inventor, and, at the same moment, from down below on the ground, came a warning cry:

But Eradicate had spoken too late. Tom pressed the switch; there was a deafening crash, a spurt of flame, and then followed wild cries and confused shouts, while the echoes of the reports rolled about the hills surrounding Shopton.

CHAPTER X

"Was anyone hurt?"

"Bless my ham sandwich!"

"I don't believe it was anything serious, Tom," said the odd man. "No one seems to be hurt." "Look at Eradicate!" suddenly exclaimed Ned.

They looked to where the young bank employee pointed, and saw the old colored man, seated on the seat of his ramshackle wagon, doing his best to pull down to a walk the big galloping mule, which was dragging the vehicle around in a circle.

But the noise of the shots had evidently frightened the longeared animal, and he was in no mood for stopping, now that he had once started. It was not until some of the workmen ran out from the group where they had gathered to watch Tom's test, and got in front of Boomerang, that they succeeded in bringing him to a halt.

"Yo'--yo're a nice one, ain't yo'?" he demanded in sarcastic tones. "Yo' done enough runnin' in a few minutes fo' a week ob Sundays, an' now I won't be able t' git a move out ob ye! I'se ashamed ob yo', dat's what I is! Puffickly ashamed ob yo'. Go 'long, now, an' yo' won't git no oats dish yeah day! No sah!" and, highly indignant, Eradicate led the now slowly-ambling mule off to the stable.

"Dat's all right, Mass a Tom," was the reply. "I done called t' you t' wait, but yo' didn't heah me, I 'spects. But it doan't mattah, now. Shoot all yo' laik, Boomerang won't run any mo' dis week. He done runned his laigs off now. Shoot away!"

"No more shooting right away," called the young inventor. "I want to see how we made out with the first round. How did she check up, Ned?"

"Yes, indeed," added Lieutenant Marbury. "The recoil was hardly noticeable, though, of course, with the full battery of guns in use, it might be more so."

The rest of that day was spent in trying out the guns, firing them with practice and service charges, though none of the shells used contained projectiles. It would not have been possible to shoot these, with the Mars held in place in the midst of Tom's factory buildings.

"I think I can say so--yes," was the answer, with a questioning look at the officer.

Ned blushed with pleasure.

"But I needed the Suggestion to start with," the young inventor replied.

"Yes, I counted on that," Tom explained. "I shall have to work out that formula, though, and be ready for it. But, on the whole, I am pretty well satisfied."

The Mars was hauled back into the shed, and the roof slid shut over the craft. Much yet remained to do on it, but now that Tom was sure the important item of armament was taken care of, he could devote his entire time to the finishing touches.

Meanwhile Lieutenant Marbury remained as Tom's guest, and was helpful in making suggestions that would enable the young inventor to meet the government's requirements.

"They are, indeed," agreed Tom. "I guess the way in which we handled that fire in the red shed sort of discouraged them."

"They're not so easily discouraged as that," he remarked. "And, with the situation in Europe growing more acute every day, I am afraid some of those foreigners will take desperate measures to gain their ends."

"Well, I think they will either try to so injure you that you will not be able to finish this aerial warship, or they will damage the craft itself, steal your plans, or damage some of your other inventions."

"They are seeking to strike at the United States through you," was the answer. "They don't want Uncle Sam to have such formidable weapons as your great searchlight, the giant cannon, or this new warship of the clouds."

"No, it is true we do not intend to go to war with any of the conflicting European nations," admitted Lieutenant Marbury, "but you have no idea how jealous each of those foreign nations is of all the others. Each one fears that the United States will cease to be neutral, and will aid one or the other."

"Yes, each nation, which may, at a moments notice, be drawn into a war with one or more rival nations, fears that we may throw in our lot with its enemies."

"That's the way I believe it will work out. So you must be careful, especially since you have taken on so many new men.

"Have they done anything to make you feel that way?" asked the lieutenant.

"And not only about your new airship and other inventions," said the officer, "but about yourself, personally. Will you do that?"

"Well, be on your guard, at all events," warned Lieutenant Marbury.

But there were a number of others, from New York, and other large cities, of whom Tom was not so sure.

"Yes, I have quite a number," Tom admitted. "But they are all good workmen. They stood the test."

"Is that so?" asked Tom. "That is news to me. I must look into this."

"No, not yet, but I shall have to shift some there from other work I think, in order to get finished on time."

"Why, have you seen anything--do you--" began the young man, for Mr. Swift had not been told of the suspicions of the lieutenant.

"I won't, Dad. Thanks for telling me. This latest craft is sure going to be a beauty."

"I'm sure of it, Dad!"

CHAPTER XI

Tom Swift pondered long and intently over what his father had said to him. He sat for several minutes in his private office, after the aged inventor had passed out, reviewing in his mind the talk just finished.

And the more Tom thought of it, the more he was convinced that such a thing was at least possible.

Tom had reached a point in his work where he could leave much to his helpers. He had several good foremen, and, with his father to take general supervision over more important details, the young inventor had more time to himself. Of course he did not lay too many burdens on his father's shoulders since Mr. Swift's health was not of the best.

"When I'm not there I'll go about in the other shops, and sort of size up the situation," he decided. "I may be able to get a line on some of those plotters, if there are any here."

As Tom was about to leave his office, to put into effect his new resolution to make a casual inspection of the other shops, he met Koku, the giant, coming in. Koku's hands and face were black with oil and machine filings.

"No accident, Master," he replied. "I help man lift that hammer-hammer thing that pounds so. It get stuck!"

"Him stuck," explained Koku simply.

"And is that what you did this time?" asked Tom.

"What man said that?"

"Well, maybe you know what you're talking about, but I don't," said Tom, with a pleasant smile at his big helper. "Come on, Koku, we'll go see what it all means."

"Well, I'll see," half promised Tom. "If it's going to get out of gear all the while it might pay me to keep you at it so you could get it back in place whenever it kicked up a fuss, and so save time. I'll see about it."

"Been having trouble here?" asked Tom, noting that the workman was one of the new hands he had hired.

"Yes," agreed Tom, "he's pretty strong. But what's this you said about wanting to give up this job, and go on the airship construction."

"I didn't intend him to repeat that to you, Mr. Swift," he said. "I was a little put out at the way this hammer worked. I lose so much time at it that I said I'd like to be transferred to the airship department. I've worked in one before But I'm not making a kick," he added quickly. "Work is too scarce for that."

"Yes, sir. I've worked on the engines, and on the planes."

"Yes, I've worked on them, too, but the engineering part is my specialty. I'm a little out of my element on a trip-hammer."

"Thank you, Mr. Swift! I'll show him all I know about it. Oh, there goes the hammer again!" he exclaimed, for, as he started it up, as Tom turned away, the big piece of steel once more jammed on the channel-plates.

"Wait a minute!" exclaimed Tom. "I want to get a look at that machine."

"So you want to be transferred to the airship department, do you? Well, we'll see about that We'll see."

Ned Newton called on his chum that evening. The two talked of many things, gradually veering around to the subject uppermost in Tom's mind--his new aircraft.

"I suppose I am," admitted Tom. "But the success of the Mars means a whole lot to me. And that's something I nearly forgot. I've got to go out to the shop now. Want to come along, Ned?"

"This is just something simple," Tom said. "It won't take long."

"But this isn't the way to the airship shed," objected the young bank clerk, as he noted in which direction Tom was leading him.

"Trouble!" exclaimed his chum. "Has that plot Lieutenant Marbury spoke of developed?"

"I had an idea," the young inventor said, "that the man at the machine let it get out of order purposely, so I'd change him. I want to see if my suspicions are correct."

"Ha! There it is!" Tom suddenly exclaimed.

"Yes. This is what's been throwing the hammer off the guides all the while," and Tom pulled out a small steel bolt that had been slipped into an oil hole. A certain amount of vibration, he explained to Ned, would rattle the bolt out so that it would force the hammer to one side, throwing it off the channel-plates, and rendering it useless for the time being.

"Do you think it was done purposely?"

"You don't mean that you'd take a fellow like that and put him to work on your new aerial warship, do you, Tom?"

"I think I have."

"But won't it be risky?"

"I think you're taking too big a risk, Tom," his chum said. "Why not discharge the man?"

"Say, old man!" exclaimed Ned, "what you want is a day off, and I'm going to see that you get it. You need a little vacation."

"Then you'll have it!" cried Ned. "There's going to be a little picnic to-morrow. Why can't you go with Mary Nestor? She'd like you to take her, I'm sure. Her cousin, Helen Randall, is on from New York, and she wants to go, also."

"Because she said so," laughed Ned. "I was over to the house to call. I have met Helen before, and I suggested that you and I would take the two girls, and have a day off. You'll come, won't you?"

"Nonsense! Give up work for one day!" urged Ned. "Come along. It'll do you good--get the cobwebs out of your head."

The next day, having instructed his father and the foremen to look well to the various shops, and having seen that the work on the new aerial warship was progressing favorably, Tom left for a day's outing with his chum and the two girls.

"Tom, you look tired," said Mary. "I'm sure you've been working too hard!"

"Yes, he is, too!" declared Ned, "and he's running more chances, too."

"Oh, that's all bosh!" laughed Tom. "Come on, let's go ashore and walk."

After a bit the couples became separated, and Tom found himself walking beside Mary in a woodland path. The girl glanced at her companion's face, and ventured:

"They're worth more than that," he replied gallantly. "I was thinking of--you."

"None at all," he assured her. "It's just a soft of notion--"

"Hark!" she whispered to Tom, "I heard someone mention your name then. Listen!"

CHAPTER XII

"What is it, Mary?" he asked in a whisper.

Tom shook his head in negation.

"I think not," was her answer. "Listen; there it is again."

"Yes," he nodded. Then, motioning to Mary to remain where she was, he stepped forward, taking care to tread only on grassy places where there were no little twigs or branches to break and betray his presence. He was working his way toward the sound of the unseen voice.

Tom saw the forms of two men, partially concealed by bushes, walking away from him. The men took no pains to conceal their movements, so Tom was emboldened to advance with less caution. He hurried to where he could get a good view, and, at the sight of one of the men, he uttered an exclamation.

"That man--I know him!" the young inventor exclaimed. "It is Feldman--the one who wanted to be changed from the trip-hammer to the airship department. But who is that with him?"

"He looks like a Frenchman, with that little mustache and imperial."

"You may know what you're talking about, but I don't, Tom," said Mary, with a smile at her companion. "Are they friends of yours?"

"Spare me the details, Tom!" interrupted Mary. "You know I don't understand a thing about machinery. The wireless you erected on Earthquake Island was as much as I could comprehend."

"And you say they are not friends of yours?"

"Then they must be enemies!" exclaimed Mary with quick intuition. "Oh, Tom, you will be careful, won't you?"

"Then why were these men discussing you?"

"They mentioned your name."

"Well, I suppose it is all right, Tom, and I surely hope it is. But you will be careful, won't you? And you look more worried than you used to. Has anything gone wrong?"

"Would you really, Tom?"

"That's awfully nice of you. But you do look worried, Tom. Has anything troubled you?"

"A fire! Oh, Tom! You never told me!"

Mary seemed much alarmed, and again begged Tom to be on his guard, which he promised to do. Had Mary known the warnings uttered by Lieutenant Marbury she might have had more occasion for worry.

"Well, it's possible. I have been warned that foreign spies are trying to get hold of some of my patents, and also to hamper the government in the use of some others I have sold. But they'll have their own troubles to get away with anything. The works are pretty well guarded, and you forget I have the giant, Koku, who is almost a personal bodyguard."

"Yes, Mary, I will," promised the young inventor. "But don't say anything to Ned about what we just saw and heard."

"Because he's been at me to hire a couple of detectives to watch over me, and this would give him another excuse. Just don't say anything, and I'll adopt all the precautions I think are needful."

"And I promise I will."

"Well, hasn't it done you good to take a day off?" Ned demanded of his chum, when they were on their homeward way.

"You swung your thoughts into a new channel, didn't you?"

But, though Tom thus passed off lightly the little incident of the day, he gave it serious thought when he was alone.

The last was easily disposed of, for, on reaching his shops that afternoon, Tom cross-questioned the colored man, and obtained a most accurate description of the odd foreigner. It tallied in every detail with the man Tom had seen in the woods.

"Yes, Feldman asked for a day off," the foreman said in response to Tom's question. "He claimed his mother was sick, and he wanted to go to see her. I knew you wouldn't object, as we were not rushed in his department."

"Over Lafayette way."

The next day Tom made it his business to pass near the hammer that was so frequently out of order. He found Feldman busy instructing Koku in its operation. Tom resolved on a little strategy.

"Very well, Mr. Swift. There doesn't seem to be any trouble at all, but it may happen any minute. Koku seems to take to it like a duck to water."

"And then am I to go into the aeroplane shop?"

"She is much better. I took a day off yesterday to go to see her," the man replied quietly enough, and without sign of embarrassment.

This time Feldman could not repress a start. But he covered it admirably by stooping over to pick up a tool that fell to the floor.

"Oh," said Tom, as he turned aside to hide a smile. He was sure now he knew at least one of the plotters

Work on the aerial warship was rushed, and it seemed likely that a trial flight could be made before the date set. Lieutenant Marbury sent word that he would be on hand when needed, and in some of the shops, where fittings for the Mars were being made, night and day shifts were working.

"Guns and all?" asked Ned, who had come over to pay his chum a visit. Mr. Damon was also on hand, invoking occasional blessings.

Ned had a little vacation from the bank, and was to stay all night, as was Mr. Damon.

"Massa Tom! Massa Tom!" yelled the excited colored man. "Git up! Git up! Suffin' turrible am happenin' in de balloon shop. Hurry! An' yo' stan' still, Boomerang, or I'll twist yo' tail, dat's what I will! Hurry, Massa Tom!"

CHAPTER XIII

Tom Swift was something like a fireman. He had lived so long in an atmosphere of constant alarms and danger, that he was always ready for almost any emergency. His room was equipped with the end in view that he could act promptly and effectively.

His first care was to throw on the main switch, connected with a big storage battery, and to which were attached the wires of the lighting system. This at once illuminated every shop in the plant, and also the grounds themselves. Tom wanted to see what was going on. The use of a storage battery eliminated the running of the dynamo all night.

All this while Eradicate was shouting away, down in the yard.

"Killing Koku!" exclaimed Tom, as he finished his hasty dressing. "Then my giant must already be in the fracas. I wonder what it's all about, anyhow."

"Your thoughts do you credit, Ned!" Tom answered. "If you listen right close, you'll hear several noises."

Tom could hear his chum bound out of bed to the floor, and, at the same time, from the big shed where Tom was building his aerial warship came a series of yells and shouts.

"I'm coming, Tom!" Ned informed his chum. "Wait a minute."

"Oh, Tom, what is it?" asked Mrs. Baggert, the housekeeper, looking from her room.

Mr. Damon, who roomed next to Ned, came out of his own apartment partially dressed.

"I think it isn't that," Tom answered. "No alarm has rung. Koku seems to be in trouble."

By this time Ned had run out into the hall, and, together, he and Tom sped down the corridor. They could not hear the shouts of Eradicate so plainly now, as he was on the other side of the house.

"What is it, Rad? What is it?" demanded the young inventor breathlessly.

"I know that--but what kind?"

From the interior of the big shed, not far from the house, Tom and Ned heard a confused jumble of shouts, cries and pleadings, mingled with the rattle of pieces of metal, and the banging of bits of wood. And, above all that, like the bellowing of a bull, was noted the rumbling voice of Koku, the giant.

"It's suah trouble, all right," went on Eradicate. "Mah mule, Boomerang, had a touch ob de colic, an' I got up t' gib him some hot drops an' walk him around, when I heard de mostest terrific racket-sound, and den I 'spected trouble was comm."

Torn was the first to reach the small door of the shed. This was built in one of the two large main doors, which could be swung open when it was desired to slide the Mars in from the ground, and not admit it through the roof.

Ned looked over his chum's shoulder and saw the giant, Koku, struggling with four men--powerful men they were, too, and they seemed bent on mischief.

"We're here, Koku!" cried Tom. "Watch for an opening, Ned!" he called to his chum.

Though such a big man, Koku was exceptionally quick, and no sooner did he see his advantage, as two of the men turned their gaze away from him, than he seized it.

So big was Koku's hands that they almost encircled the necks of his antagonists. Then happened a curious thing.

"He's choking them to death!" shouted Ned.

A moment later, with a quick and sudden motion he bent his arms, bringing toward each other the two men he held as captives. Their heads came together with a dull thud, and a second later Koku allowed two limp bodies to slip from his grip to the floor.

The giant grunted, and then, with a quick motion, slung himself around, hoping to bring the enemies at his back within reach of his powerful arms. But there was no need of this.

"There they go!" cried Ned.

As he approached nearer to the unconscious captives Tom uttered a cry of surprise, for he recognized them as two of the new men he had employed.

He glanced toward the window through which the two men had jumped to escape, and he was just in time to see one of them run past the open door. The face of this one was under a powerful electric light, and Tom at once recognized the man as Feldman, the worker who had had so much trouble with the trip-hammer.

The giant, bending over the men he had knocked unconscious by beating their heads together, seemed little worse for the attack.

CHAPTER XIV

Little time was lost in securing the two men who bad been so effectively rendered helpless by Koku's ready, if rough, measures. One of them was showing signs of returning consciousness now, and Tom, not willing to inflict needless pain, even on an enemy, told one of his men, summoned by the alarm, to bring water. Soon the two men opened their eyes, and looked about them in dazed fashion.

"It must have been a thunderbolt," spoke the other dreamily. "But it didn't look like a storm."

The men put their hands to their heads, and seemed to comprehend. They looked at the rope that bound their feet. Their forearms had been loosened to allow them to take a drink of water.

"It looks as though he had the best of us, whether we did or not," said the man Tom knew as Kurdy. "Whew, how my head aches!"

"Not half as sorry as we are," returned Ransom ruefully.

"Oh, trust Feldman for getting away," sneered Kurdy. "He always leaves his friends in the lurch."

The two captives looked at one another, sitting bound on the floor of the shop, their backs against some boxes.

"Perhaps it would be better," said Tom quietly. "Eradicate," he went on, to the colored man, "go to the house and tell Mrs. Baggert that everything is all right and no one hurt."

"Well, they're not hurt much," and Tom permitted himself a little smile. "I don't want my father to worry. Tell him everything is all right."

"Who else besides Feldman got away?" asked Tom, looking alternately at the prisoners.

"We might as well give up, I tell you," spoke Kurdy to Ransom.

"Who was the fourth man?" Tom repeated.

"Harrison, who has been working on the motor?" cried the young inventor.

"I'm sorry to learn that," Tom went on in a low voice. "He was an expert in his line. But what was your object, anyhow, in attacking Koku?"

"But I don't understand why you came into this shed at night," went on Tom. "No one is allowed in here. You had no right, and Koku knew that. What did you want?"

"Succeeded in what?" demanded the young inventor.

Tom gave a surprised whistle.

"Yes, he's one of the foreign spies," interrupted Ransom. "You'd find it out, anyhow, if we didn't tell you. They are after you, Tom Swift, and after your machines. They had vowed to get them by fair means or foul, for some of the European governments are desperate."

"Then we must try to capture them," decided Tom. "Ned, see if the chase had any results. I'll look after these chaps--Koku and I."

"Do you mean that you four came into this shop, at midnight, to damage the Mars?" asked Tom.

"Harrison, Feldman, Ransom and I came in, thinking the coast was clear. But Koku must have seen us enter, or he suspected we were here, for he came in after us, and the fight began. We couldn't stop him, and he did for us. I'm rather glad of it, too, for I never liked the work. It was only that they tempted me with a promise of big money."

"That Frenchman--La Foy, he calls himself, and some other foreigners in your shops."

"Bless my chest protector!" cried Mn Damon, who had come in and had been a silent listener to this. "Can it be possible?"

"Are they friendly among themselves?" asked Tom.

"Tell me more about it," urged Tom.

"Then my suspicions of him were justified," thought Tom. "He evidently met La Foy in the woods to make plans. But Koku and Eradicate spoiled them."

The four conspirators had managed, by means of a false key, and by disconnecting the burglar alarm, to enter the airship shed. They were about to proceed with their work of destruction when Koku came on the scene.

Of course he attacked them at once, and they sprang at him. Then ensued a terrific fight. Eradicate, arising to doctor his mule, as he had said, heard the noise, and saw what was going on. He gave the alarm.

"No, they got away, Tom. I had a lot of your men out helping me search the grounds, but it wasn't of much use."

"What do you mean?"

"I'm with you, Tom."

"I'll do the best I can," said Tom, gently, making no promises.

A further search was made in the morning for the two conspirators who had escaped, but no trace of them was found. Tom then realized why Feldman was so anxious to be placed in the aeroplane department--it was in order that he might have easier access to the Mars.

"Probably I am hitting some of the innocent in punishing those who, if they had the chance, would become guilty," Tom said to his chum, "but it cannot be helped--I can't afford to take any chances."

"But there may be more," he warned the young inventor. "You are not done with them yet."

"Well, I guess we re ready," he finally announced. "All aboard!"

"Nonsense!" exclaimed Tom. "You're not going to back out at the last minute. All aboard! Cast off the ropes!" he cried to the assistants.

CHAPTER XV

"Well, Tom, we're moving!" cried Ned Newton, clapping his chum on the back, as he stood near him in the pilot-house. "We're going up, old sport!"

"Well, I wasn't quite sure," Ned confessed. "You know you were so worried about--"

"Bless my pin cushion!" cried Mr. Damon, as he looked over the rail at the earth below. "We're moving fast, Tom."

"Just how fast do you think you can travel when you are in first-class shape?" asked Lieu tenant Marbury, as he noted how the Mars was behaving on this, the first trip.

"That will more than satisfy the government requirements," the officer said. "But, of course, your craft will have to come up to expectations and requirements in the matter of armament."

Up and up went the big dirigible aerial warship. Had you been fortunate enough to have seen her you would have observed a craft not unlike, in shape, the German Zeppelins. But it differed from those war balloons in several important particulars.

Amidships, suspended below the great bag, were the living and sleeping quarters, where food was cooked and served and where those who operated the craft could spend their leisure time. Extra supplies were also stored there.

There was also an arrangement in the motor compartment, so that the ship could be steered and operated from there. This was in case the forward pilot-house should be shot away by an enemy. And, also, in the motor compartment were the sleeping quarters for the crew.

At the extreme end of the big bag were the various rudders and planes, designed to keep the craft on a level keel, automatically, and to enable it to make headway against a strong wind. The motive power consisted of three double-bladed wooden propellers, which could be operated together or independently. A powerful gasoline engine was the chief motive power, though there was an auxiliary storage battery, which would operate an electrical motor and send the ship along for more than twentyfour hours in case of accident to the gasoline engine.

"You don't seem to have forgotten anything, Tom," said Ned admiringly, as they soared upward.

"Are you going far?" asked Mr. Damon.

"Oh, no, I'm not frightened!" exclaimed the odd man. "Bless my suspenders, no! But I promised my wife I'd be back this evening, and

"No, don't do that! Don't! I beg of you!" cried Mr. Damon. "You see--er--Tom, my wife doesn't like me to make these trips. Of course, I understand there is no danger, and I like them. But it's just as well not to make her worry-you understand!"

"No, it certainly is not," agreed Lieutenant Marbury, "and I am interested in seeing how you will overcome the recoil."

Meanwhile the Mars, having reached a considerable height, being up so far, in fact, that the village of Shopton could scarcely be distinguished, Tom set the signal that told the engine-room force to start the propellers. This would send them ahead.

"Well she seems to run all right," observed Lieutenant Marbury, as the big craft surged ahead just below a stratum of white, fleecy clouds.

They had been running for perhaps ten minutes when Tom shoved over the hand of an indicator that communicated with the engineroom from the pilot-house. At once the Mars increased her speed.

"Bless my-hat! I should say so!" cried Mr. Damon, for he was standing outside the pilot-house just then, on the "bridge," and the sudden increase of speed lifted his hat from his head.

"Thanks! Guess I'd better tie it fast," remarked the odd man, putting his hat on tightly.

"And now suppose we get ready for the gun tests," suggested Tom, when they had been running for about an hour.

"Well, I'm not making any rash promises," Tom went on, "but I think we can turn the trick."

But the main deck guns could be elevated to an angle of nearly forty-five degrees, so they could take care of nearly any hostile aircraft that approached.

"Here they are," spoke Tom, as he pointed to a space in the middle of the main cabin floor. He lifted a brass plate, and disclosed three holes, covered with a strong wire netting that could be removed. "The bombs will be dropped through those holes," explained the young inventor, "being released by a magnetic control when the operator thinks he has reached a spot over the enemy's city or fortification where the most damage will be done. I'll show you how they work a little later. Now we'll have a test of some of the guns."

Service charges had been put in, though, of course, no projectiles would be used, since they were then flying over a large city not far from Shopton.

He and Lieutenant Marbury were beside a gun, and were about to fire it, when suddenly, from the stern of the ship, came a ripping, tearing sound, and, at the same time, confused shouts came from the crew's quarters.

"One of the propellers!" was the answer. "It's split, and has torn a big hole in the gas bag!"

All on board the Mars became aware of a sudden sinking sensation.

CHAPTER XVI

Above the noise of the machinery in the motor room could be heard the thrashing and banging of the broken or loose propellerblade. Just what its condition was, could not be told, as a bulge of the gas bag hid it from the view of those gathered about the gun, which was about to be fired when the alarm was given.

"That's nothing," was the cool answer. "It is only for a moment. Only a few of the gas compartments can be torn. There will soon enough additional gas in the others to lift us again."

"We're not falling so fast now," observed Ned.

"It might have been much worse, my boy!" exclaimed the lieutenant. "That's a great arrangement of yours--the automatic gas machine."

"In a trolley car, you see," Tom went on, when the excitement had calmed down, "as soon as the air pressure in the tanks gets below a certain point, caused by using the air for a number of applications of the brakes, it lets a magnetized bar fall, and this establishes an electrical connection, starting the air pump. The pump forces more air into the tanks until the pressure is enough to throw the pump switch out of connection, when the pump stops. I use the same thing here."

"For the time being, yes. But we must unship that damaged propeller, and go on with the two."

As several spare ones were carried aboard one could be put on in place of the broken one, had this been desired. But Tom thought the accident a good chance to see how his craft would act with only two-thirds of her motive force available, so he did not order the damaged propeller replaced. When it was lowered to the deck it was carefully examined.

"That's a question I can't answer," Tom replied. "There may have been a defect in the wood, but I had it all carefully examined before I used it."

"Did something hit it; or did it hit something?" asked Ned as he saw Tom carefully examining the broken blades.

"You don't mean to say you're going to keep on, and with the balloon damaged; are you?" cried Mr. Damon, in surprise.

"Bless my necktie!" ejaculated the odd man.

There really was very little danger in proceeding. The Mars was just as buoyant as before, for more gas had been automatically made, and forced into the uninjured compartments of the bag. At the same time enough sand ballast had been allowed to run out to make the weight to be lifted less in proportion to the power remaining.

So, after a little while, during which it was seen that the Mars was proceeding almost normally, the matter of discharging the guns was taken up again.

The two big weapons were discharged together, and for a moment after the report echoed out among the cloud masses every soul on the ship feared another accident had happened.

"What's the matter?" cried Ned. "Something go wrong?"

"Are you sure they are strong enough?" asked Lieutenant Marbury.

"Bless my watch chain!" cried Mr. Damon. "You aren't going to fire those guns again; are you, Tom?"

"No danger! Don't you call nearly upsetting the ship danger?"

"Excuse me!" said Mr. Damon firmly. "I'd rather go down, if it's all the same to you. If my wife ever knew I was here I'd never hear the last of it!"

"No, I certainly would not," was the prompt answer. "I am sorry, too, for they seemed to be just what was needed. Of course I understand this is not an official test, and I am not obliged to make a report of this trial. But had it been, I should have had to score against you.

Preparations were now made for firing the four-inch guns once more. All this while the Mars had been speeding around in space, being about two miles up in the air. Tom's craft was not designed to reach as great an elevation as would be possible in an aeroplane, since to work havoc to an enemy's fortifications by means of aerial bombs they do not need to be dropped from a great height.

On the other hand, in destroying buildings, it has been found desirable to drop a bomb from a good height so that it may penetrate even a protected roof, and explode inside.

"Well, something's wrong, that's sure," remarked Tom, in rather disappointed tones as he noted the effect of the second shots. "If we get as much recoil from the two guns, what would happen if we fired them all at once?"

"I won't--just at present," Tom said, ruefully. "I'm afraid I'll have to begin all over again, and proceed along new lines."

"Oh, I'll get busy on it right away," Tom declared. "We'll go down now, and start right to work. I'm afraid, Ned, that our idea of a door-spring check isn't going to work."

"Oh, the idea is all right," declared Tom, "but it wants modifying. There is more power to those recoils than I figured, though our first experiments seemed to warrant us in believing that we had solved the problem."

"Yes, there can't be any recoil from that," Tom said. "I'll drop a few blank ones, and see how accurate the range finders are.

CHAPTER XVII

Dropping bombs from an aeroplane, or a dirigible balloon, is a comparatively simple matter. Of course there are complications that may ensue, from the danger of carrying high explosives in the limited quarters of an airship, with its inflammable gasoline fuel, and ever-present electric spark, to the possible premature explosion of the bomb itself. But they seem to be considered minor details now.

The law of velocity governing falling bodies is well known. It varies, of course, according to the height, but in general a body falling freely toward the earth, as all high-school boys know, is accelerated at the rate of thirty-two feet per second. This law has been taken advantage of by the French in the present European war. The French drop from balloons, or aeroplanes, a steel dart about the size of a lead pencil, and sharpened in about the same manner. Dropping from a height of a mile or so, that dart will acquire enough velocity to penetrate a man from his head all the way through his body to his feet.

At aeroplane meets there are often bomb-dropping contests, and balls filled with a white powder (that will make a dust-cloud on falling, and so show where they strike) are used to demonstrate the birdman's accuracy.

"You're not going to use real bombs, are you, Tom?" asked Ned.

"Here is the range-finder and the speed calculator," the young inventor went on as he indicated the various instruments. "The operator sits here, where he can tell when is the most favorable moment for releasing the bomb."

"I have first to determine where I want to drop the bomb," Tom explained, "and then I have to get my distance from it on the range-finder. Next I have to know how fast I am traveling, and how far up in the air I am, to tell what the velocity of the falling bomb will attain at a certain time. This I can do by means of these instruments. some of which I have adapted from those used by the government," he said, with a nod to the officer.

"We will now assume that the bombs are in place in the holes in the floor of the cabin," Tom went on. "As I sit here I have before me three buttons. They control the magnets that hold the bombs in place. If I press one of the buttons it breaks the electrical current, the magnet no longer has any attraction, and it releases the explosive. Now look down. I am going to try and drop a chalk bomb near that stone fence."

"Here she goes!" cried Tom, as he made some rapid calculations from his gauge instruments. There was a little click and the chalk bomb dropped. There was a plate glass floor in part of the cabin, and through this the progress of the pasteboard bomb could be observed.

"Did I? You just watch. I had to allow for the momentum that would be given the bomb by the forward motion of the balloon."

"There it goes?" cried the lieutenant. "You did the trick, Swift!"

In succession they were released from the bottom of the cabin, at other designated objects. The second one was near a tree. It struck within five feet, which was considered good.

Down went the cardboard bomb, and so good was the aim of the young inventor that the white dust arose in a cloud directly back of the scarecrow.

"Why, that was a man! Bless my pocketbook!" cried Mr. Damon.

"Well, it proved the accuracy of your aim, at any rate," observed Lieutenant Marbury. "The bomb dropping device of your aerial warship is perfect--I can testify to that."

"What's next?" asked Mr. Damon, looking at his watch. "I really ought to be home, Tom."

"Bless my stovepipe, no, Tom! My wife would have hysterics. Just land me at Shopton and I'll take a car home."

A safe landing was made, and the Mars once more put away in her hangar. Mr. Damon departed for his home, and Lieutenant Marbury again took up his residence in the Swift household.

"Not so very well. Too much recoil from the guns.

"No, Dad!" Tom cried. "I'm going to make this work. I never had anything stump me yet, and I'm not going to begin now!"

"Yes I will, Dad! You just wait."

"Just what are you trying to find out, Tom?" asked Ned, a few nights later, when he found his chum looking at the broken parts of the propeller.

Tom was "poking" away amid splinters, and bits of broken wood, when he suddenly uttered an exclamation, and held up something. "Look!" he cried. "I believe I've found it."

"The thing that weakened the propeller. Look at this, and smell!" He held out a piece of wood toward Ned. The bank employee saw where a half-round hole had been bored in what remained of the blade, and from that hole came a peculiar odor.

"That's it!" cried Tom. "Someone bored a hole in the propeller, and put in some sort of receptacle, or capsule, containing a corrosive acid. In due time, which happened to be when we took our first flight, the acid ate through whatever it was contained in, and then attacked the wood of the propeller blade. It weakened the wood so that the force used in whirling it around broke it."

"As sure as I am that I'm here! Now I know what caused the accident!"

"Yes, I know we might," said Tom. "It must be the work of some of those foreign spies whose first plot we nipped in the bud. I must tell Marbury of this, but don't mention it to dad."

Lieutenant Marbury agreed with Tom that someone had surreptitiously bored a small hole in the propeller blade, and had inserted a corrosive acid that would take many hours to operate. The hole had been varnished over, probably, so it would not show.

But they did not prove to be. A careful examination showed nothing wrong. An effort was made to find out who had tried to destroy the Mars in midair, but it came to nothing. The two men in custody declared they knew nothing of it, and there was no way of proving that they did.

The guns there were made double, with the extra barrel filled with water or sand, that could be shot out as was the regular charge. As both barrels were fired at the same time, and in opposite directions, with the same amount of powder, one neutralized the other, and the recoil was canceled, the ship remaining steady after fire.

"Good luck to you!" cried Ned.

Finally the new guns were made, and tried with the Mars held on the ground. They behaved perfectly, the shooting of sand or water from the dummy barrel neutralizing the shot from the service barrel.

"I sure am!"

"But why start at night?" asked Ned.

The Mars flew slowly all night, life aboard her, at about the level of the clouds, going on almost as naturally as though the occupants of the cabins were on the earth. Excellent meals were served.

"Tell you in the morning," replied Tom, with a smile.

"Why, Tom! We're over the ocean!" he cried.

CHAPTER XVIII

Surprise, for the moment, held Mr. Damon, Ned and Lieutenant Marbury speechless. They looked from the heaving waters of the ocean below them to the young pilot of the Mars. He smiled at their astonishment.

"That's right," chimed in Mr. Damon. "Bless my nightcap! If I had known I was going to be brought so far away from home I'd never have come."

"Then you didn't travel fast during the night?" asked the government man.

"Well, we're over the ocean all right," spoke Ned, as he looked down at the heaving waters.

"No, it isn't the first time we've taken a water flight," spoke Ned. "I was only surprised at the suddenness of it, that's all."

"About ten miles out, yes," admitted Tom. "Far enough to make it safe to test the guns with real projectiles. That is what I want to do."

"Yes, but at slow speed. The engines are in better shape now than ever before," Tom said. "Well, if you're ready we'll have breakfast."

"So you're going to give the guns a real test this time, is that it, Tom?" asked Ned, as he pushed back his plate, a signal that he had eaten enough.

"But don't you think it's a bit risky out over the water this way. Supposing something should--should happen?" Ned hesitated.

"Yes; or turn upside down."

"No, thank you!" interrupted Mr. Damon, as he looked below. There was quite a heavy swell on, and the ocean did not appear very attractive. They would be much more comfortable in the big Mars.

"We'll soon know," spoke Tom. "I'm going to get ready for the test now.

As service charges were to be used, and as the projectiles were filled with explosives, great care was needed in handling them.

To make the test a severe one, small floating targets were first dropped overboard from the Mars. Then the aerial warship, circling about, came on toward them. Tom, seated at the rangefinders, pressed the button that released the shells containing the explosives. One after another they dropped into the sea, exploding as they fell, and sending up a great column of salt water.

"That's good," responded Tom. "But the others won't be so easy. We have nothing to shoot at."

One after another the guns were loaded. As has been explained, they were now made double, one barrel carrying the projectile, and the other a charge of water.

"All ready," answered Ned.

"Nonsense! What for?"

"Nothing will happen. Look out now, I'm going to fire."

"Here they go!" exclaimed the young inventor.

As the projectile was fired in one direction, and the water in one directly opposite, the two discharges neutralized one another.

"Well!" cried Tom as the echoes died away. "How was it?"

"I'm glad to hear you say so. There are one or two little things that need changing, but I really think I have about what the United States Government wants."

"Well?" asked Tom suggestively.

"I think we've seen the last of them," Tom declared. "Now we'll go on with the tests."

For some little time longer they remained out over the sea, going through some evolutions to test the rudder control, and then as their present object had been accomplished Tom gave orders to head back to Shopton, which place was reached in due time.

"Successful, Dad, in every particular."

Tom ripped it open with a single gesture, and in a flash his eyes took in the words. He read:

The message was signed with a name Tom did not recognize.

"No--oh, no," replied Tom, as he crumpled up the paper and thrust it into his pocket. "No bad news, Dad."

When Tom showed the message to Lieutenant Marbury, that official, after one glance at the signature, said:

"Who's Pierson?" asked Tom.

Extra precautions were taken about the shops. Strangers were not permitted to enter, and all future work on the Mars was kept secret. Nevertheless, Tom was worried. He did not want his work to be spoiled just when it was about to be a success. For that it was a success, Lieutenant Marbury assured him. The government man said he would have no hesitation in recommending the purchase of Tom's aerial warship.

"What is that?" Tom inquired.

"You shall!" declared the young inventor.

One dull gray morning Tom roused his friends early and announced that the Mars was going up.

And even as the flight began, the forerunning wind and rain came in a gust of fury. Into the midst of it shot the big aerial warship, with her powerful propellers beating the moisture-laden air.

CHAPTER XIX

"Of course I am! What do you mean?"

"Well, I mean are you sure your craft will stand all this straining, pulling and hauling?" went on Ned, as he clung to a brass hand rail, built in the side of the pilot-house wall for the very purpose to which it was now being put.

"Well, it's taking a big chance, it seems to me," went on Ned, as he peered through the rain-spotted bull's-eyes of the pilothouse.

"Are you going to do that, Tom?"

"Well, Tom, you know best, of course," admitted Ned. "But to me it seems like taking a big risk."

The storm grew worse as the day progressed, until it was a veritable hurricane of wind and rain. The warnings of the Weather Bureau had not been exaggerated. But through the fierce blow the Mars fought her way. As Tom had said, she was going with the wind. This was comparatively easy. But what would happen when she headed into the storm?

"Do you--do you think we are in any danger?" he finally asked.

"You mean we will be--later?"

"Bless my accident insurance policy!" murmured Mr. Damon. "I wish I had stayed home. If my wife ever hears of this--" He did not seem able to finish the sentence.

As hour succeeded hour and nothing happened, the timid ones aboard began to take more courage. Tom never for a moment lost heart. He knew what his craft could do, and he had taken her up in a terrific storm with a definite purpose in view. He was the calmest person aboard, with the exception, perhaps, of Koku. The giant did not seem to know what fear was. He depended entirely on Tom, and as long as his young master had charge of matters the giant was content to obey orders.

"We'll have our hands full when we turn around and head into the wind," he said to his chum. "That will be enough."

"I surely am. I don't want any comebacks from Uncle Sam after he accepts my aerial warship. I've guaranteed that she'll stand up and make headway against a gale, and I'm going to prove it"

"I rather guess those foreign spies have given up trying to do Tom an injury," remarked Ned to the lieutenant as they sat in the main cabin, listening to the howl of the wind, and the dash of the rain.

"But we haven't seen anything of the spies," Ned remarked.

"They must be desperate."

"Take care of yourselves now," advised the young aero-inventor, as he entered the cabin, finding it hard work to close the door against the terrific wind pressure.

"Because we are going to turn around and fight our way back against the gale. We may be turned topsy-turvy for a second or two."

"No, not that exactly. But watch out!"

At first no change was noticeable. So strong was the force of the wind that it seemed as though the Mars was going in the same direction. But Ned, noticing a direction compass on the wall, saw that the needle was gradually shifting.

"Can you get her around?" cried the lieutenant above the roar of the gale.

Inch by inch he fought the big craft through the storm. Inch by inch the indicator showed the turning, until at last the grip of the gale was overcome.

And the Mars was. There was no doubt of it. She had succeeded, under Tom's direction, in changing squarely about, and was now going against the wind, instead of with it.

But Tom himself scarcely had reckoned on the force of his craft, for as the propellers whirled more rapidly the aerial warship did begin to make headway, and that in the teeth of a terrific wind.

"I believe she is," agreed the lieutenant.

The Mars, so far, had met every test. Tom had decided on ten minutes more of gale-fighting, when from the tube that communicated with the engine-room came a shrill whistle.

"Yes," called Ned into the mouthpiece. "What's the matter?"

CHAPTER XX

Ned repeated the message breathlessly.

"Wouldn't it be better to turn about, and run before the wind, so as not to put too great a strain on the machinery?" asked Lieutenant Marbury.

Ned and the government man took the wheel, while Tom hurried along the runway leading from the pilot-house to the machinery cabin. The gale was still blowing fiercely.

"What happened?" he asked, noting that already the principal motive power was coming from the big storage battery. The shift had been made automatically, when the main motor gave out.

"Think you put too heavy a load on the motor?" Tom asked.

"Well, no use trying to fight this gale with the storage battery," Tom said, after a moment's thought. "We'll run before it. That's the easiest way. Then we'll try to rise above the wind."

As he bent over the burned-out motor, looking at the big shiny connections, he saw something that startled him. With a quick motion Tom Swift picked up a bar of copper. It was hot to the touch--so hot that he dropped it with a cry of pain, though he had let go so quickly that the burn was only momentary.

"Matter!" cried Tom. "A whole lot is the matter! That copper bar is what made the short circuit. It's hot yet from the electric current. How did it fall on the motor connections?"

For a moment Tom did not know what to think, and then, as the memory of that warning telegram came to him, he had an idea.

"Not that I know of," was the answer.

But a careful search revealed no one. Yet the young inventor was sure the bar of copper, which had done the mischief of short-circuiting the motor, had been put in place deliberately.

He looked at the height gauge on the wall of the motor-room, and noted that the Mars was going up. In accordance with Tom's instructions they were sending her above the storm area. Once there, with no gale to fight, they could easily beat their way back to a point above Shopton, and make the best descent possible.

"What was it, Tom?" asked Ned, coming back to join his chum, after George Ventor, the assistant pilot, had taken charge of the wheel.

"Your enemies came aboard?"

"Then let's make a search and find them, Tom. It must be some of those foreign spies."

But a more careful search of the craft than the one Tom had casually made revealed the presence of no one. All the crew and helpers were accounted for, and, as they had been in Tom's service for some time, they were beyond suspicion. Yet the fact remained that a seemingly human agency had acted to put the main motor out of commission. Tom could not understand it.

"It's worse than queer," declared Tom, "it's alarming! I don't know when I'll be safe if we have ghosts aboard."

"Well, when we can't find out who put that bar in place I might as well admit it was a ghost," spoke Tom. "Certainly, if it was done by a man, he didn't jump overboard after doing it, and he isn't here now. It sure is queer!"

In due time the Mars, having fought her way above the storm, came over Shopton, and then, the wind having somewhat died out, she fought her way down, and, after no little trouble, was housed in the hangar.

"I'll just tell him we had a slight accident, and let it go at that," Tom decided. "No use in causing him worry."

"I'm going to keep careful watch over the aerial warship, at any rate," declared Tom. "If there's a hidden enemy aboard, I'll starve him out."

It took nearly a week to repair the big motor, and, during this time, Tom put some improvements on the airship, and added the finishing touches.

Meanwhile several little things occurred to annoy Tom. He was besieged with applications from new men who wanted to work, and many of these men seemed to be foreigners. Tom was sure they were either spies of some European nations, or the agents of spies, and they got no further than the outer gate.

"And yet, with all my precautions, they may get me, or damage something," declared Tom. "It is very annoying!"

So impressed was Ned with the necessity for caution that he arranged to take his vacation at this time, so as to be on hand to help his chum, if necessary.

The night before the trip the guards about the airship shed were doubled, and Tom made two visits to the place before midnight. But there was no alarm.

"She certainly is a beauty," said Captain Warner, as the big craft shot upward. "I shall be interested in seeing how she stands gun fire, though."

It was after supper of the first day out, and our friends were seated in the main cabin laying out a program for the next day, when sudden yells came from a part of the motor cabin devoted to storage. Koku, who had been sent to get out a barrel of oil, was heard to shout.

"Oh, Master! Come quickly!" cried the giant. "There are many men here. There are stowaways aboard!"

CHAPTER XXI

"Stowaways!"

From the engine compartment, back of the amidship cabin, came a sound of cries and heavy blows. The yells of Koku could be heard above those of the others.

What he said was in French, as Tom understood, though he knew little of that language. Also, what the Frenchman said produced an immediate result, for the men following him sprang at our friends with overwhelming fierceness.

Against such odds little could be done, though our friends did not give up without a struggle.

His words were lost in smothered tones, for one of his assailants put a heavy cloth over his mouth, and tied it there, gagging him. Another man, with a quick motion, whipped a rope about Tom's hands and feet, and he was soon securely bound.

Of the riot of thoughts that ran through the heads of each one, I leave you to imagine.

These were only a few of the questions Tom asked himself, as he lay there, bound and helpless. Doubtless Mr. Damon and the others were asking themselves similar questions.

It had been a rough-and-tumble fight, by which our friends were made prisoners, but no one seemed to have been seriously, or even slightly, hurt. The invaders, under the leadership of the Frenchman, were rather ruffled, but that was all.

"I hope I have not had to hurt any of you," the Frenchman observed, with sarcastic politeness. "I regret the necessity that caused me to do this, but, believe me, it was unavoidable."

"He's one of the foreign spies," thought Tom "and he's got us and the ship, too. They were too many for us!"

"I am going to treat you as well as I can under the circumstances. You and your other friends, who are also made prisoners, will be allowed to be together, and then you can talk to your hearts' content."

"Ah!" thought Tom. "This is the leader of the gang that attacked Koku in the shop that night. They have been waiting their chance, and now they have made good. But where did they come from? Could they have boarded us from some other airship?"

"If you will but have patience a little longer," went on La Foy, for that was evidently the name of the leader, "you will all be together. We are just considering where best to put you so that you will not suffer too much. It is quite a problem to deal with so many prisoners, but we have no choice."

"We are going to put you all together in the largest storeroom, which is partly empty," La Foy said. "There you will be given food and drink, and treated as well as possible under the circumstances. You will also be unbound, and may converse among yourselves. I need hardly point out," he went on, "that calling for help will be useless. We are a mile or so in the air, and have no intention of descending," and he smiled mockingly.

Night had fallen, but the cabin was aglow with electric lights. The foreigners in charge of the Mars seemed to know their way about perfectly, and how to manage the big craft. By the vibration Tom could tell that the motor was running evenly and well.

A moment later several of the foreigners entered. Some of them did not look at all like Frenchmen, and Tom was sure one was a German and another a Russian.

As La Foy spoke, he opened a storeroom door that led off from the main, or amidship, cabin. This room was intended to contain the supplies and stores that would be taken on a long voyage. It was one of two, being the larger, and now contained only a few odds and ends of little importance. It made a strong prison, as Tom well knew, having planned it.

"On second thought," said La Foy, as he saw Koku being placed with his friends, "I think we will keep the big man with us. We had trouble enough to subdue him. Carry him back to the engineroom."

"Now then," said La Foy to his prisoners, as he stood in the door of the room, "I will unbind one of you, and he may loose the bonds of the others."

CHAPTER XXII

For a moment or two, after the ropes binding his hands were loosed, Tom Swift did nothing. He was not only stunned mentally, but the bonds had been pulled so tightly about his wrists that the circulation was impeded, and his cramped muscles required a little time in which to respond.

"I--I'll loosen you all in lust a second," he said, as he bent over to pick at the knot of the rope around his legs. His own voice sounded strange to him.

Tom found it no easy matter to loosen the bonds on his feet. The ropes were well tied, and Tom's fingers were stiff from the lack of circulation of blood. But finally he managed to free himself. When he stood up in the dim storeroom, that was now a prison for all save Koku, he found that he could not walk. He almost toppled over, so weak were his legs from the tightness of the ropes. He sat down and worked his muscles until they felt normal again.

"Bless my wristlets, Tom! What does it all mean?"

"Oh, well, Tom, anyone might have been fooled by those plotting foreigners," said Mr. Damon. "Now, we'll try to turn matters about and get the best of them. Oh, but it feels good to be free once more!"

"Well, if this isn't the limit I don't know what is!" cried Ned Newton.

"Are they really foreign spies?" asked Captain Warner.

"Is that what they did?" asked Mr. Damon.

"Well, that's about the way it was," answered the engineer. "We were working away, making some adjustments, oiling the parts and seeing that everything was running smoothly, when, all at once, I heard Koku yell. He had gone in the oil room. At first I thought something had gone wrong with the ship, but, when I looked at the giant, I saw he was being attacked by four strange men. And, before I, or any of the other men, could do anything, they all swarmed down on us.

"They burst in on us in the same way," Tom explained. "But where did they come from? Where were they hiding?"

"That's it," decided Tom. "But I don't understand how they got in. The hangar was well guarded all night."

"Yes, that is so," admitted Tom, and, later, he learned that such had been the case. The foreign spies, for such they were, had managed to corrupt one of Tom's trusted employees, who had looked the other way when La Foy and his fellow-conspirators sneaked into the airship shed and secreted themselves.

"Bless my fountain pen!" cried Mr. Damon. "There's only one thing to do!"

"Why, get out of here, call a policeman, and have these scoundrels arrested. I'll prosecute them! I'll have my lawyer on hand to see that they get the longest terms the statutes call for! Bless my pocketbook, but I will!" and Mr. Damon waxed quite indignant.

He looked around the storeroom, which was then their prison. It was illuminated by a single electric light, which showed some boxes and barrels piled in the rear.

"Oh, we'll get out," declared Ned confidently, "but I don't believe we'll find a policeman ready to take our complaint. The upper air isn't very well patrolled as yet."

"Yes, worse luck," returned the young inventor. "I feel foolish when I think how we let them take us prisoners."

"Very little," said Engineer Mound. "They were desperate fellows. They know something about aircraft, too. For, as soon as Koku, Ventor and I were disposed of, some of them went at the machinery as if they had been used to running it all their lives."

"Well, they seem to be running her, all right," admitted the young inventor, "and at good speed, too. They have increased our running rate, if I am any judge."

"That's so!" agreed Mr. Damon. "What is to become of us? They may heave us overboard into the ocean!"

"We must be, by this time," spoke Tom. "We were headed in that direction, and we have come almost far enough to put us somewhere over the Atlantic, off the Jersey coast."

"We won't try to swim until we have to," he said. "Now, let's take an account of stock, and see if we have any means of getting out of this prison.

CHAPTER XXIII

"Not a thing!" exclaimed Mr. Damon. "Not a blessed thing! They have even taken my keys and--my fountain pen!"

"So is mine," echoed Tom.

"They evidently knew what they were doing," said Lieutenant Marbury. "I don't usually carry a revolver, but of late I have had a small automatic in my pocket. That's gone, too."

"Well," if we haven't any weapons, or means of getting out of here, we must make them," said Tom, as hopefully as he could under the circumstances. "I don't know all the things that were put in this storeroom, and perhaps there may be something we can use."

"Well, there isn't any water in here, or anything to eat, of so much I am sure," went on Tom "So we will have to depend on our captors for that."

They all agreed that this might not be a bad plan, and were preparing to raise a united shout, when there came a knock on the door of their prison.

"What do you mean by reason?" asked Tom bitterly. "You have no right to impose any conditions on us."

"Which kind--yours or ours?" asked Tom pointedly.

"We are in sufficient force to cope with you. I think you have seen that." He spoke calmly and in perfect English, though with a marked accent. "My men are armed, and will stand here ready to meet violence with violence," he went on. "Is that understood?"

"I think it will be better to give in to him at least for a while," said Captain Warner in a low voice to Tom. "We need water, and will soon need food. We can think and plan better if we are well nourished."

"For the time being--yes."

"Our answer is--yes," spoke Tom. "We will not try to get out-just yet," he added significantly.

"Keep back from the door!" was the stern command of La Foy. "The food and drink will be passed in only if you keep away from the entrance. Remember my men are armed!"

While the guards looked on, others of the "pirate crew," as Ned dubbed them, passed in food and water. Then the door was locked again.

No one felt much like eating, however, so the food was put away for a time. And then, somewhat refreshed, they began looking about for some means of getting out of their prison.

"Yes, and they could turn some of your own quick-firers on us," added Captain Warner. "No, we must work quietly, I think, and take them unawares, as they took us. That is our only plan."

That plan was deemed best, and preparations made for spending the night in their prison.

Once they were all awakened by a violent plunging of the airship. The craft seemed to be trying to stand on her head, and then she rocked violently from side to side, nearly turning turtle. "What is it?" gasped Ned, who was lying next to Tom.

"I think the latter is the case," observed Lieutenant Marbury.

The first gray streaks of dawn finally shone through the only window of their prison. Sore, lame and stiff, wearied in body and disturbed in mind, the captives awoke. Tom's first move was toward the window. It was high up, but, by standing on a box, he could look through it. He uttered an exclamation.

"We are away out over the sea," spoke Tom, "and in the midst of a bad storm."

CHAPTER XXIV

"A storm," repeated Ned. "What sort?"

"Bless my galvanometer!" cried Mr. Damon. "Then we are out over the ocean again, Tom?"

"What part?" asked the assistant pilot.

"Suppose I take a look?" suggested Captain Warner. "I've done quite a bit of sailing in my time."

"There isn't a landmark in sight," he announced. "We might be over the middle of the Atlantic, for all I could tell."

"How's that?" asked Ned.

"Yes, it seems to be a combination of European nations against us," admitted Captain Warner. "Probably, after they have made good their seizure of Tom's aerial warship, they will portion her out among themselves, or use her as a model from which to make others."

"Undoubtedly," was the captain's answer. "It has been the object of these foreign spies, all along, not only to prevent the United States from enjoying the benefits of these progressive inventions, but to use them for themselves. They would stop at nothing to gain their ends. It seems we did not sufficiently appreciate their power and daring."

"If they don't heave us overboard half-way there," commented Ned, in rather gloomy tones

"Well, we must do something," declared Lieutenant Marbury. "Come, it's daylight now, and we can see to work better. Let's see if we can't find a way to get out of this prison. Say, but this sure is a storm!" he cried, as the airship rolled and pitched violently.

"Well, let's eat something, and set to work," proposed Ned.

Tom and his companions indignantly demanded to be released, but their protests were only laughed at, and while the guards stood with ready weapons the door was again shut and locked.

"What is it--a way out?" asked Lieutenant Marbury anxiously.

"Hurray!" cried Ned. "That's the ticket! Now we'll soon show these fellows what's what!"

"That is so," agreed Captain Warner. "We must use strategy."

"Here," said Tom, indicating a place far back in the room. "We can work there in turns, sawing a hole through the wall. It will bring us out in the passage between the aft and amidship cabins, and we can go either way."

While the aerial warship pitched and tossed in the storm, over some part of the Atlantic, Tom and his friends took turns in working their way to freedom. With the sharp end of the file a small hole was made, the work being done as slowly as a rat gnaws, so as to make no noise that would be heard by their captors. In time the hole was large enough to admit the end of the saw.

Meanwhile they had been given food and water at intervals, but to all demands that they be released, or at least told why they were held prisoners, a deaf ear was turned.

The Mars continued to fly through the air. Sometimes, as Tom and his friends could tell by the motion, she was almost stationary in the upper regions, and again she seemed to be flying at top speed. Occasionally there came the sound of firing.

"Do you suppose they are being attacked?" asked Ned, hopefully.

Later our friends learned that such was the case.

All the while they were secretly working to gain their freedom so they might attack and overpower their enemies, they took occasional observations from the small window. But they could learn nothing of their whereabouts. They could only view the heaving ocean, far below them, or see a mass of cloud-mist, which hid the earth, if so be that the Mars was sailing over land.

"Well, we have fuel and supplies aboard for nearly two weeks," Tom answered.

"No, we'll be out of here before then!" declared Lieutenant Marbury.

Their set night as the time for making the attempt--late at night, when it was hoped that most of their captors would be asleep.

"We'll do it at midnight," announced Tom.

"We must be running into another storm. Feel how she heaves and rolls!"

"It sure is a storm!" cried Ned, "and a heavy one, too," for there came a burst of thunder, that seemed like a report of Tom's giant cannon.

As Tom reached up to switch on the electric light again, there came a flash of lightning that well nigh blinded them. And so close after it as to seem simultaneous, there came such a crash of thunder as to stun them all. There was a tingling, as of a thousand pins and needles in the body of each of the captives, and a strong smell of sulphur. Then, as the echoes of the clap died away, Tom yelled:

CHAPTER XXV

For a moment there was silence, following Tom's wild cry and the noise of the thunderclap. Then, as other, though less loud reverberations of the storm continued to sound, the captives awoke to a realization of what had happened. They had been partially stunned, and were almost as in a dream.

"Bless my soul! What has happened?" cried Mr. Damon.

"We seem to be falling!" exclaimed Lieutenant Marbury.

Indeed, it was evident that the Mars was sinking rapidly. To all there came the sensation of riding in an elevator in a skyscraper and being dropped a score of stories.

"We've stopped falling!" he cried. "The automatic gas machine is pumping. Part of the gas bag was punctured, but the unbroken compartments hold!"

"It's a non-burnable gas," Tom quickly explained. "But come on. This may be our very chance. There seems to be something going on that may be in our favor."

He made for the sawed panel, and, in another instant, had burst out and was through it, out into the passageway between the after and amidship cabins. His companions followed him.

"What has happened?" cried Ned. "What does it all mean?,'

The Mars seemed to have passed completely through a narrow storm belt. She was now in a quiet atmosphere, though behind her could be seen the fitful play of lightning, and there could be heard the distant rumble of thunder.

His friends needed no further urging. Jerry Mound and the machinist rushed to the engine-room, to look after any of the enemy that might be there, while Tom, Ned and the others ran into the middle cabin.

But none were needed. So stunned were the foreigners by the lightning bolt, which had miraculously passed our friends, and so unnerved by the striking down of La Foy, their leader, that they seemed like men half asleep. Before they could offer any resistance they were bound with the same ropes that had held our friends in bondage. That is, all but the big Frenchman himself. He seemed beyond the need of binding.

"We found him chained up," Jerry explained, as the big giant, freed from his captivity, rubbed his chafed wrists.

"Only those two knocked out by the lightning," the engineer explained. "We've made them secure. I see you've got things here in shape."

"They no let anything happen. I be in chains all the while," the giant answered. "Jump on me before I can do anything!"

The bound ones were carried to the same prison whence our friends had escaped, but their bonds were not taken off, and Koku was put in the place with them. By this time La Foy and the two other stricken men showed signs of returning life. They had only been stunned.

The craft had only been slightly damaged by the lightning bolt, though three of the gas bag compartments were torn, The others sufficed, however, to make the ship sufficiently buoyant.

The prisoners had no chance to escape, and, indeed, they seemed to have been broken in spirit. La Foy was no longer the insolent, mocking Frenchman that he had been, and the two chief foreign engineers seemed to have lost some of their reason when the lightning struck them.

"That's right," agreed his chum.

"And now what are you going to do, Tom?" asked Ned, when, once more, they had the airship to themselves.

And, in due time, this was done. Tom added some improvements to the aircraft, making it better than ever, and when she was given the test required by the government, she was an unqualified success, and the rights to the Mars were purchased for a large sum. In sailing, and in the matter of guns and bombs, Tom's craft answered every test.

"Yes, Tom," replied the aged inventor, "I admit I was wrong."

"The Mars will be the naval terror of the seas in any future war," predicted Captain Warner.

It was Tom's enemies who had set on fire the red shed, and who later tried to destroy the ship by putting a corrosive acid in one of the propellers. That plot, though, was not wholly successful. Then came the time when one of the spies hid on board, and dropped the copper bar on the motor, short-circuiting it. But for the storage-battery that scheme might have wrought fearful damage. The spy who had stowed himself away on the craft escaped at night by the connivance of one of Tom's corrupt employees.

It came out at the trial that one of Tom's most trusted employees had proved a traitor, and had the night before the test, allowed the foreign spies to secrete themselves on board, to rush out at an opportune time to overpower our hero and his friends. But luck was with Tom at the end.

"I don't know," was the slow answer. "I think a self-swinging hammock, under an apple tree, with a never-emptying pitcher of ice-cold lemonade would be about the thing."

"Well, come on, let's begin now," laughed Tom. "I need a vacation, anyhow."

End of Project Gutenberg's Etext of Tom Swift And His Aerial Warship

By VICTOR APPLETON

TOM SWIFT AND HIS MOTOR CYCLE TOM SWIFT AND HIS MOTOR BOAT TOM SWIFT AND HIS AIRSHIP TOM SWIFT AND HIS SUBMARINE BOAT TOM SWIFT AND HIS ELECTRIC RUNABOUT TOM SWIFT AND HIS WIRELESS MESSAGE TOM SWIFT AMONG THE DIAMOND MAKERS TOM SWIFT IN THE CAVES OF ICE TOM SWIFT AND HIS SKY RACER TOM SWIFT AND HIS ELECTRIC RIFLE TOM SWIFT IN THE CITY OF GOLD TOM SWIFT AND HIS AIR GLIDER TOM SWIFT IN CAPTIVITY TOM SWIFT AND HIS WIZARD CAMERA TOM SWIFT AND HIS GREAT SEARCHLIGHT TOM SWIFT AND HIS GIANT CANNON TOM SWIFT AND HIS PHOTO TELEPHONE TOM SWIFT AND HIS AERIAL WARSHIP TOM SWIFT AND HIS BIG TUNNEL TOM SWIFT IN THE LAND OF WONDERS TOM SWIFT AND HIS WAR TANK TOM SWIFT AND HIS AIR SCOUT TOM SWIFT AND HIS UNDERSEA SEARCH TOM SWIFT AMONG THE FIRE FIGHTERS TOM SWIFT AND HIS ELECTRIC LOCOMOTIVE

BY VICTOR APPLETON

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