Page:The Development of Navies During the Last Half-Century.djvu/235

great was the risk of discovery when close, and the consequent danger of being sunk by the fire of the ship attacked, that ideas turned in the direction of a torpedo which could be discharged at a vessel from a moderate distance. This resulted in the fish torpedo. The original conception was that of a small sort of boat propelled along the surface and carrying a charge of gunpowder in the bow. An Austrian officer broached this idea to Mr Whitehead, an English civil engineer settled in that country. From this crude proposal he developed the wonderful piece of mechanism now universally known as the Whitehead torpedo. First, he had to fix upon his mode of propulsion. He selected compressed air, working a small engine and a screw in the tail of his fish, as in an ordinary vessel. Steam would condense, and had other disadvantages; gunpowder gas could not be controlled; electricity was not applicable. The result has shown that his choice was a good one. Then he determined that his torpedo should travel under water. An explosion on the surface and against the water line of a ship would have little effect, because most of the gas generated would escape into the air. Immersed, the surrounding water confines the gas and compels it to exert all its energy against the bottom of the ship. If the charge is large enough, this pent-up energy is irresistible. It was desirable, therefore, that the torpedo should strike a ship a certain distance below the water line, keeping this depth during its passage. Now, any vessel containing compressed air has an appreciable weight added to it, but as the air is allowed to