"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."