“That crazy fellow,” uttered Jacob Farnum, “had some mania on his mind that we were all great sinners, and that he’d save the whole lot of us by killing us under water.”

“It seems strange,” muttered Hal, “for even a crazy man to have the nerve to destroy himself slowly in such a way.”

“Humph, no; nothing new in that line,” returned Mr. Farnum.

“What are we going to do with him, sir?” inquired Captain Jack.

“Well, we’re not going to turn in at any of the coast towns to give him up,” replied the builder.  “We’ll keep right along until we join the fleet, and then we’ll ask the advice of some naval officer.”

When, at last, all had become accustomed to the world to which they had returned, Hal and Eph went below, to turn on the gasoline power a short time the “Pollard” was kicking the water at the exhilarating gait of eighteen miles an hour.

“How did it come, sir, that you made it eighteen miles, instead of knots?” asked Captain Jack, after a while.

“Why, that’s the basis on which gasoline engines are built,” replied Mr. Farnum.  “For that matter, captain, when we’ve had more practice with this boat we’ll tune the engine up to eighteen full knots an hour.  In the second boat we are going to try for an assured speed of twenty-two to twenty-four knots.”

“It seems to me,” said Jack, musingly, “that the ideal submarine torpedo boat ought to have a speed of from twenty-eight, to thirty-five knots.”

“Why?”

“So that the speed of the submarine boat shall always be ahead of the speed of any battleship afloat.”

“Again, why?”

“Why, so that the submarine can give effective chase to a battleship.”

“But submarines are intended only to go with fleets of their own country, or else to remain on station at or near the mouths of harbors to be defended.”

“All well and good,” argued Captain Jack, nodding.  “In future wars a battleship fleet is likely to keep away from any harbor known to be defended by the enemy’s submarine boats.  But, if a submarine torpedo boat could have speed enough to give chase to a fleeing battleship, and sink when within range of the battleship’s guns, yet still be able to pursue, under water, and destroy the battleship, that would mean the day when battleships wouldn’t be of any further use, wouldn’t it?”

“Undoubtedly,” admitted Mr. Farnum.  “But you see, captain, so far as present human ingenuity goes, a boat can’t be built to sail as fast under water as another can be made to go on the surface.”

“But that’s the problem I’m going to tackle, as soon as I get our plans a little further along,” murmured David Pollard, eagerly.  “Benson is right.  When we get a submarine boat that can pursue the fastest battleship, on the surface or below it, then the United States, with a hundred such submarines, could defy the combined naval powers of the world.  If the United States can own a large fleet of such boats, then we can control the seas of the world.”