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 shore.