The torpedo is a terrible but uncertain weapon. The modern search-light makes daylight of the darkest night, and renders the approach of a torpedo-boat within striking distance exceedingly difficult. If detected, the boat is doomed, for a concentration of fire from the larger ship beats the necessarily small assailant to death in a moment. Moreover it is by no means sure that the torpedo will do its work when launched at the enemy, even if it succeeds in piercing the wire net that is suspended to entangle it at a safe distance from the hull of the vessel attacked. Summing up all the obstacles to successful torpedo attack, it may be reckoned that _only one in twelve_ reaches its mark, explodes, and accomplishes its purpose. It remained for the twentieth century to produce a terrible fighting-machine--often foretold but never perfected until the Russo-Japanese war--which should approach the enemy unseen, discharge its torpedo with careful aim at the most vulnerable part of its huge adversary, and, while the latter was floating in fancied security on the open sea, strike a blow which should be instantly fatal. Such is the marvellous submarine torpedo-boat of this day and generation. The idea of a boat that shall move under water and discharge its missile at a hostile ship is by no means a new one. In 1776 a young man named David Bushnell, of New Haven, Connecticut, constructed a submarine boat resembling two "turtle-backs" screwed together. She was so small that only one man could occupy her. Air was supplied to last half an hour. The "crew," who was expected to work by hand the propelling screw, was also supposed to be able to pump in and out water ballast to enable her to descend to the desired depth, to maintain the craft on an even keel when submerged, and to detach two hundred pounds of ballast weights in order to rise again to the surface. An explosive mine containing one hundred and fifty pounds of gunpowder was to be towed alongside until the bottom of the enemy's ship was reached, when, the mine having been fastened to the hull, a clock-work arrangement, set by the operator, would explode the charge. Nothing practical resulted from the young Yale man's scheme, but it is evident that his boat was the original model for every submarine torpedo-boat which has since been invented. In 1800 Robert Fulton, turning his attention from steam engines for a while, modelled a boat which was a considerable improvement upon Bushnell's, but, like the latter, failed in practical use. During our Civil War several essays were made at submarine warfare, the Confederates taking the initiative. One of these submarines actually blew up a Union man-of-war, but was itself demolished, with its crew of nine men. Every great navy in the world now reckons a number of submarines among its available forces.