At different times during the development of torpedo warfare there have been many attempts to construct and perfect submarine boats of different types, but in no case has an attempt to use one been successful. The United States corvette Housatonic was sunk off Charleston Harbor in 1864 by a submarine torpedo-boat, but there are excellent reasons for believing that she was at the time of the attack used as an ordinary surface-boat with a bow-torpedo on a spar. In most cases the boats used, or rather designed, have been propelled by hand-power, their rate of speed being very low. Attempts are being made in all countries to perfect some form of submarine boat, and, judging from the experimental success attained heretofore, it is fair to suppose that some type will finally prove successful, although in any case its use would be extremely limited. DRIFTING TORPEDOES. Torpedoes of this description have been used in great numbers in time of war, but only with indifferent success. The especial function of the drifting torpedo is the destruction of vessels lying at anchor, the torpedo being sent adrift at a convenient point and allowed to float either at the surface or by means of a buoy at some distance below, and by the action of the current to be carried into contact with the vessel, being exploded by a contact-fuse. There is no especial shape considered superior for this type, and generally the torpedoes are extemporized from the most convenient materials at hand. Of the many types that have been tried there are two which may be considered especially dangerous. The first of these is a torpedo intended to be dropped by a vessel being chased, to be caught by the one in her wake. This type may be described in general as two torpedoes of a size sufficient to contain 20 or 30 lbs. of dynamite, connected by a rope or light chain bridle, and floated by flat water-colored buoys. Dropped from the stern of a vessel, the bridle is caught by the bow of the chaser, and the torpedoes being swept alongside explode against the bilges. _Lewis’s Drifting Torpedo._ [Illustration: Lewis’s Beam Torpedo.]