Two classes of vessels stand forward prominently as the products of the twentieth century. One is the _Dreadnought_, or all-big-gun one-calibre type of battleship, the other is the submarine. The fact that both are the result of the slow developments of centuries does not render them the less the products of the last few years. Both are untried in battle, and they are regarded as preparing the way for the introduction respectively of surface and under-water warships, the power of which is conjecturable only. Associated with both is the torpedo. The dream of a submarine which shall travel faster than a surface vessel of the same size is never likely to be realised, provided that the surface vessel is built for speed also, for the simple reason that the vessel travelling on the surface has only about a third of its surface in connection with the water, whereas the submarine has its whole surface submerged, and has three times as much friction against the water to overcome. Hence, a lightly armed, very fast vessel is regarded as likely to play an important role in the navy of the not distant future, and finds its representative in the destroyer of to-day. The submarine and the destroyer owe their existence to the battleship’s greatest enemy, the torpedo. All three vessels carry that weapon, and any two of them may combine against the third. The spar-torpedo was such an unsatisfactory weapon at best that it had either to be abandoned, save under most unusual circumstances, or improved out of all recognition. The possibilities of the torpedo itself were so great as to compel its retention, and the startling proposition was made that torpedoes should be fired by under-water guns at a distant ship. The blowing up of the _Albemarle_ in the American Civil War showed what could be accomplished by a small fast steam launch. If this could be done with a spar-torpedo, how much more destructive would a torpedo be which could be directed against a hostile vessel from a small fast launch which could approach to within an effective range, and then turn and make a rush for safety from the gun-fire which might be brought to bear in her direction. Several torpedoes of one kind and another have been designed, but they have all had to give way to the Whitehead torpedo. The inventor is stated to have derived his idea in 1864 from a fire-boat designed by an Austrian officer, who thought of loading a small boat with explosives, to be fired by a pistol connected with protruding spars which should strike the vessel attacked, while the fire-boat itself was to be propelled by a screw driven by clockwork. Whitehead improved on this by making his boat of iron, and able to travel under water for a short distance at a speed of six knots. Its explosive was a few pounds of dynamite. By 1870 he had improved this to a torpedo having a speed of eight knots, a range of 400 yards, and a charge of 76 lb. of gun-cotton. The modern Whitehead torpedo