"That's what struck me," Tom answered, as he continued to drive the Hawk earthward. "They thought they were doing a smart trick--imitating the tactics of the Allies with their tanks--but they must be color blind."

Ned took another observation through the gla.s.ses. He could see the tank more easily now. There she was, fairly well hidden in a clump of bushes and small trees on the banks of a river, about a hundred miles away from Shopton. It was in a wild and desolate country, and only with the airship could the trail have thus been followed.

Ned saw that the tank had been daubed with green, yellow, and brown paint, in fantastic blotches, to make the big machine blend with the foliage; and, to a certain extent, this had been accomplished.

But, as Ned had remarked, the green used was of too vivid a hue. No natural tree put forth leaves like that, and the gla.s.s had further revealed the error.

"Look, Tom!" suddenly cried Ned. "She's moving!"

"You're right!" answered the young inventor. "They've seen us and are trying to get away."

"But they can't beat your airship, Tom."

"I know that. But their game--Oh, Ned, they're going to wreck her!"

cried Tom, and there was anguish in his voice.

As the two looked down from their seats In the Hawk they saw the tank, in its fantastic dress of splotchy paint, leave her lair amid the bushes and trees, and head toward the river. Like some ponderous prehistoric monster about to take a drink, she careened her way toward the stream, which, at this point, ran between high banks.

"What's the game?" cried Ned.

"They're going to send her to smash!" cried Tom. "She's pretty tough, Tom, but she'll never stand a tumble down into the river without breaking a lot of machinery inside her."

"But if they demolish the tank they'll kill themselves, won't they?

And Koku and your men, too, who must be prisoners in her!"

"They won't risk their own worthless hides, you may be sure of that!"

exclaimed Tom.

"There they go, but they must have left Koku and the others to their fate!"

"Oh, if they could only get loose and take control now, Tom, they'd save your tank for you!" shouted Ned.

"Yes; but they can't, I'm afraid. They may be killed, or so securely bound that they can't get loose!"

"Can't you get the Hawk there in time to stop her?"

"I'm afraid not. By that time she'll have attained top speed and it would be taking our lives in our hands to try to make a flying jump, get inside, and shut off the motors."

"Then the tank's got to smash!" said Ned gloomily.

Tom did not answer for a moment. He and his chum watched the fleeing figures running away from the war engine. What the plotters had done, as soon as they saw the aircraft and realized that Tom had discovered them, was to start the motors and leap from the tank, closing the doors after them. Whether or not they had left Koku and the others prisoners inside remained to be seen.

But the tank was plunging her way toward the steep bank of the river, doomed, it seemed, to great damage, if not to destruction.

"Oh, if we could only halt her!" murmured Ned.

Tom Swift was busy with some apparatus on the Hawk. Ned heard the hum of an electric motor which was connected with the engine, and there soon sounded the crackle of the wireless.

"What are you doing? Signaling for help from those inside the tank?"

asked Ned, for the big machine was fitted to receive and send messages of this sort.

"I'm trying something more desperate than that," Tom answered.

Again the wireless crackled, Tom working it with one hand while, with the other, he guided the aircraft. Ned looked downward with wondering eyes.

The tank was still plunging her way toward the steep bank of the river.

If she tumbled down this, there would be little left of the expensive and complicated machinery inside.

"The rascals did their work well," mused Ned. "They've probably gotten all the secrets they want and now they're going to spoil all Tom's hard work. It's a shame! If only--"

Ned ceased his musing. Something was taking place down below that he could not explain. The tank seemed to be slackening her progress. More and more slowly she approached the edge of the cliff.

"Tom! Tom!" yelled Ned. "You must have waked some of them up inside and they've thrown the motors out of gear! Hurrah! She's stopping!"

"I believe she is!" yelled Tom. "Oh, if it only works!"

The tank was still moving, though more slowly. Still the crackle of the wireless was heard.

And then, just as Tom shut off his own motor and let the Hawk glide on her downward way in a volplane to earth, the great, ponderous tank came to a stop, on the very edge of the precipice at the foot of which rolled the river.

"Whew!" whistled Ned, as the aircraft rolled along the ground near the war machine. "That was touch and go, Tom! They stopped her just in time."

"You mean the wireless stopped her," said Tom quietly. "I'm very much afraid that if Koku and the others are alive they're still prisoners in the craft."

"The wireless!" gasped Ned, as he and his chum got out of the Hawk. "Do you mean that you stopped her by wireless, Tom?"

"That's what I did. It was a desperate chance, but I took it. I had just installed in the tank a system of wireless control, so she could be guided as some torpedos and submarines are, by wireless impulses from the sh.o.r.e.

"Only I'd never given the tank system a tryout. It was all installed, and had worked perfectly on the small model I constructed. And when I saw her running away, out of control as she was, I realized the wireless was the only thing that would stop her, if that would. It might operate just opposite to what I wanted, though, and increase her speed."

"But I took the chance. I set the airship wireless current to working, and tuned it in to coincide with the control of the tank. Then, by means of the wireless impulse I shut off the motors, which can be stopped or started by hand or by electricity. I shut 'em off."

"And only just in time!" cried Ned. "Whew, Tom Swift, but that was a close call!"

"I realize that myself!" said the young inventor. "This is a new idea and has to be worked out further for our newer tanks."

"Gee!" e.j.a.c.u.l.a.t.ed Ned. "Out of date before got into use! Now let's see about our friends!"

It was the work of but a moment to enter the tank, and, after making sure that the machinery was all right, Tom and Ned made their way to the interior. In one of the smallest rooms they found Koku and the others bound with ropes, and in a bad way. Koku was so tied with cords and hemp as to resemble a bale of Manilla cable.

"Cut 'em loose, Ned!" cried Tom, and the bonds were soon severed. Then came explanations.

As has been told, one of the plotters, whose ident.i.ty was not learned until later, came with the forged note. The giant and Tom's men set out in the tank, and the machine was stopped at a certain place where the plotter, who gave the name of Crossleigh, told them Tom was to meet his men.

Out of ambush leaped Simpson and others, who overpowered the mechanics, even subduing Koku after a fierce fight, and then they took possession of the tank, making the others prisoners.

What happened after that could only be conjectured by Tom's men, for they were shut up in an inner room. It seemed certain, though, that the tank was taken to some secret place and there painted to resemble the verdure. Then she went on again, coming to rest where Tom and Ned saw her.