Torpedoes may be divided into four classes, viz.:--
1.--Drifting or floating torpedoes. 2.--Towing torpedoes. 3.--Locomotive torpedoes. 4.--Outrigger or spar torpedoes.
_Drifting or Floating Torpedoes._--By "drifting" or "floating" torpedoes are meant all those submarine machines which are dependent on the tide or current of a stream for their action and motion.
During the American civil war this mode of attacking vessels was constantly employed by the Confederates, and though not successful in destroying any of the Federal ships, was the means of considerably hampering the movements of their river flotillas.
Drifting torpedoes might be advantageously used for the destruction of pontoon bridges, booms, &c., and in this way, had the Turks in their late war used them, the Russians would have found the crossing of the Danube a matter of infinite danger and difficulty; in fact, by a systematic use of such weapons, combined with a little dash on the part of the Ottoman flotilla on the Danube, that river should have been to the Russians an impassable barrier. To use these torpedoes most effectively, especially against a single vessel, a thorough knowledge of the force and direction of currents should be gained before proceeding to undertake an operation in which these submarine weapons are used.
Another point to be remembered is, that if such a torpedo were started with the flood, for example, towards an enemy, and did not explode, there would be a chance of its being returned to the starting-place by the ebb tide.
In this class the following torpedoes seem the most practicable:--
1.--Lewis's drifting torpedo. 2.--McEvoy's drifting torpedo. 3.--American extempore drifting torpedo.
_Description of Lewis's Drifting Torpedo._--"Lewis's" drifting torpedo, designed for the express purpose of destroying booms or other floating obstructions placed round a vessel at anchor for the purposes of defence, is shown at Fig. 101. It consists of a box _a_, containing the charge and fitted with several detonating fuzes. This box is attached to one side of a beam _b_, and within 6 inches of one extremity, the beam being about 20 feet long and 7 inches square; to the opposite side, of the same end of the beam _b_ a heavy weight _c_, resting in a shoe _d_, is attached by a long iron rod _e_, which reaches to the other extremity of the beam, and is there connected to a bell-crank lever and spring _f_, a pressure on which detaches the weight _c_; a chain _g_, 18 feet long, connects the weight loosely with the upper end of the beam, and another chain _h_, 9 feet 6 inches long, connects it with a point more than 2 feet below the centre of the beam. The apparatus is so constructed that it floats nearly vertical with the top of the beam just above the surface of the water.