The torpedo, he quickly discovered, was a Whitehead—a powerful and deadly engine in use by all the navies of the world.
It was about seventeen feet long and a foot and a half in diameter. Torpedoes of this nature are constructed to run under the surface at any required depth down to twenty feet. A propeller and compressed air furnishes the motive power, and as the air becomes exhausted, the torpedo rises higher and higher. With the air shut off and engine stopped, the cylinder rises to the surface. As that was the case in the present instance, it seemed certain that the motive power of this particular torpedo had been nearly exhausted.
The Grampus, being constructed for work in time of war, had torpedo tubes and one torpedo aboard. Matt had studied the mechanism of the Whitehead, and he was able to proceed intelligently in his present dilemma. If there was still any air in the big tube, he might use it to carry him to the north and east, in the direction taken by the Grampus.
The lever, he discovered, which locked the engine was standing erect, while the "tripper," which worked automatically the instant the torpedo was discharged and put it under its own power, was lying flat on the curved side.
Before trying to get the compressed air in the shell to working, he swam to the blunt end of the torpedo and removed the small propeller that manipulated the firing pin. By this wise move he rendered harmless the explosive within the shell.
Swimming back, he mounted his queer raft by means of the rope loops, lifted the "tripper," and depressed the starting lever.
The twin screws, placed tandem fashion at the stern, began slowly to revolve. Heading the point of the tube north by east, he began one of the strangest rides that had ever fallen to his lot.
As the air within became more and more depleted, the steel cylinder rose higher and higher in the water.
For a lad so deeply in love with motors as was Matt, the novelty of that ride could not fail to appeal to him. He was safe, at least for a time, and felt sure that ultimately he would gain the shore or be picked up by a coastwise ship. As for the Grampus, there were cool heads and steady nerves aboard of her, and the submarine's safety would be looked after. Besides, the mysterious foes had failed in their night's work, and there was probably no more danger to be apprehended from them.
As Matt held himself astride his queer craft, guiding it by a pull this way and that, he fell to thinking of the manner in which he had been hurled into the sea.