"What was it?" gasped Mary, and, to her surprise, she found herself close to Ned, clutching his arm.

"I have an idea, but I'd rather let Tom tell you," he answered.

"But where's it going?" asked Mr. Nestor. "What in the world does Tom Swift mean by inviting us out here to witness a test, and then nearly running us down under a Juggernaut?"

"Oh, there must be some mistake, I'm sure," returned his daughter. "Tom didn't intend this."

"But, bless my insurance policy, look at that thing go! What in the world is it?" cried Mr. Damon.

The "thing" was certainly going. It had careened from the road, tilted itself down into a ditch and gone on across the fields, lights shooting from it in eccentric fashion.

"Maybe we'd better take after it," suggested Mr. Nestor. "If Tom is--"

"There, it's stopping !" cried Ned. "Come on!"

He sprang from the automobile, helped Mary to get out, and then the two, followed by Mr. Damon and Mr. Nestor, made their way across the fields toward the big object where it had come to a stop, the rumbling and roaring ceasing.

Before the little party reached the strange machine--the "runaway giant," as they dubbed it in their excitement--a bright light flashed from it, a light that illuminated their path right up to the monster. And in the glare of this light they saw Tom Swift stepping out through a steel door in the side of the affair.

"Are you all right?" he called to his friends, as they approached.

"All right, as nearly as we can be when we've been almost scared to death, Tom," said Mr. Nestor.

"I'm surely sorry for what happened," Tom answered, with a relieved laugh. "Part of the steering gear broke and I had to guide it by operating the two motors alternately. It can be worked that way, but it takes a little practice to become expert."

"I should say so!" cried Mr. Damon. "But what in the world does it all mean, Tom Swift? You invite us out to see something--"

"And there she is!" interrupted the young inventor. "You saw her a little before I meant you to, and not under exactly the circumstances I had planned. But there she is!" And he turned as though introducing the metallic monster to his friends.

"What is she, Tom?" asked Ned. "Name it!"

"My latest invention, or rather the invention of my father and myself," answered Tom, and his voice showed the love and reverence he felt for his parent. "Perhaps I should say adaptation instead of invention," Tom went on, "since that is what it is. But, at any rate, it's my latest--dad's and mine--and it's the newest, biggest, most improved and powerful fighting tank that's been turned out of any shop, as far as I can learn.

"Ladies--I mean lady and gentlemen--allow me to present to you War Tank A, and may she rumble till the pride of the Boche is brought low and humble!" cried Tom.

"Hurray! That's what I say!" cheered Ned.

"That's what I have been at work on lately. I'll give you a little history of it, and then you may come inside and have a ride home."

"In that?" cried Mr. Damon.

"Yes. I can't promise to move as speedily as your car, but I can make better time than the British tanks. They go about six miles an hour, I understand, and I've got mine geared to ten. That's one improvement dad and I have made."

"Ride in that!" cried Mr. Nestor. "Tom, I like you, and I'm glad to see I've been mistaken about you. You have been doing your bit, after all; but--"

"Oh, I've only begun!" laughed Tom Swift.

"Well, no matter about that. However much I like you," went on Mr. Nestor, "I'd as soon ride on the wings of a thunderbolt as in Tank A, Tom Swift."

"Oh, it isn't as bad as that!" laughed the young scientist. "But neither is it a limousine. However, come inside, anyhow, and I'll tell you something about it. Then I guess we can guide it back. The men are repairing the break."

The visitors entered the great craft through the door by which Tom had emerged. At first all they saw was a small compartment, with walls of heavy steel, some shelves of the same and a seat which folded up against the wall made of like powerful material.

"This is supposed to be the captain's room, where he stays when he directs matters." Tom explained. "The machinery is below and beyond here."

"How'd you come to evolve this?" asked Ned. "I haven't seen half enough of the outside, to say nothing of the inside."

"You'll have time enough," Tom said. "This is my first completed tank. There are some improvements to be made before we send it to the other side to be copied.

"Then they'll make them in England as well as here, and from here we'll ship them in sections."

"I don't see how you ever thought of it!" exclaimed the girl, in wonder.

"Well, I didn't all at once," Tom answered, with a laugh. "It came by degrees. I first got the idea when I heard of the British tanks.

"When I had read how they went into action and what they accomplished against the barbed wire entanglements, and how they crossed the trenches, I concluded that a bigger tank, one capable of more speed, say ten or twelve miles an hour, and one that could cross bigger excavations--the English tanks up to this time can cross a ditch of twelve feet--I thought that, with one made on such specifications, more effective work could be done against the Germans."

"And will yours do that?" asked Ned. "I mean will it do ten miles an hour, and straddle over a wider ditch than twelve feet?"

"It'll do both," promptly answered Tom. "We did a little better than eleven miles an hour a while ago when I yelled to you to get out of the way just now. It's true we weren't under good control, but the speed had nothing to do with that. And as for going over a big ditch, I think we straddled one about fourteen feet across back there, and we can do better when I get my grippers to working."

"Grippers!" exclaimed Mary.

"What kind of trench slang is that, Tom Swift?" asked Mr. Damon.

"Well, that's a new idea I'm going to try out It's something like this," and while from a distant part of the interior of Tank A came the sound of hammering, the young inventor rapidly drew a rough pencil sketch.

It showed the tank in outline, much as appear the pictures of tanks already in service--the former simile of two wedge- shaped pieces of metal put together broad end to broad end, still holding good. From one end of the tank, as Tom drew it, there extended two long arms of latticed steel construction.

"The idea is," said Tom, "to lay these down in front of the tank, by means of cams and levers operated from inside. If we get to a ditch which we can't climb down into and out again, or bridge with the belt caterpillar wheels, we'll use the grippers. They'll be laid down, taking a grip on the far side of the trench, and we'll slide across on them."

"And leave them there?" asked Mr. Damon.

"No, we won't leave them. We'll pick them up after we have passed over them and use them in front again as we need them. A couple of extra pairs of grippers may be carried for emergencies, but I plan to use the same ones over and over again."

"But what makes it go?" asked Mary. "I don't want all the details, Tom," she said, with a smile, "but I'd like to know what makes your tank move."

"I'll be able to show you in a little while," he answered. "But it may be enough now if I tell you that the main power consists of two big gasolene engines, one on either side. They can be geared to operate together or separately. And these engines turn the endless belts made of broad, steel plates, on which the tank travels. The belts pass along the outer edges of the tank longitudinally, and go around cogged wheels at either end of the blunt noses.

"When both belts travel at the same rate of speed the tank goes in a straight line, though it can be steered from side to side by means of a trailer wheel in the rear. Making one belt--one set of caterpillar wheels, you know--go faster than the other will make the tank travel to one side or the other, the turn being in the direction of the slowest moving belt. In this way we can steer when the trailer wheels are broken."

"And what does your tank do except travel along, not minding a hail of bullets?" asked Mr. Nestor.

"Well," answered Tom, "it can do anything any other tank can do, and then some more. It can demolish a good-sized house or heavy wall, break down big trees, and chew up barbed-wire fences as if they were toothpicks. I'll show you all that in due time. Just now, if the repairs are finished, we can get back on the road--"

At that moment a door leading into the compartment where Tom and his friends were talking opened, and one of the workmen said:

"A man outside asking to see you, Mr. Swift."

"Pardon me, but I won't keep you a moment," interrupted a suave voice. "I happened to observe your tank, and I took the liberty of entering to see

"Simpson!" cried Ned Newton, as he recognized the man who had been up the tree. "It's that spy, Simpson, Tom!"