It is not improbable that I have given a false impression concerning the relative merits of the several methods which were developed for fighting the submarine. Destroyers, patrol boats, subchasers, and mystery ships all accomplished great things in solving the most baffling problem presented by the war. The belief is general that the most successful hunter of the submarine was the destroyer, and, so far as absolute figures are concerned, this is true. Destroyers, with their depth charges and their gunfire, sank more U-boats than any other agency. One type of craft, however, proved a more destructive enemy of the submarine than even the destroyer. That was a warship of whose achievements in this direction little has so far been heard. The activities of the German submarine have completely occupied public attention; and this is perhaps the reason why few newspaper readers have suspected that there were other than German and Austrian submarines constantly operating at sea. Everyone has heard of the U-boats, yet how many have heard anything of the H-boats, the E-boats, the K-boats, and the L-boats? The H-, E-, and K-boats were British submarines, and the L-boats were American submarines. In the destruction of the German under-water craft these Allied submarines proved more successful than any kind of surface ship. The Allied destroyers, about 500 in number, sank 34 German submarines with gunfire and depth charges; auxiliary patrol craft, such as trawlers, yachts, and the like, about 3,000 in number, sank 31; while the Allied submarines, which were only about 100 in number, sank 20. Since, therefore, the Allies had about five times as many destroyers as submarines at work, it is evident that the record of the latter vessels surpasses that of the most formidable surface anti-submarine craft.
Thus the war developed the fact that the most deadly enemy of the submarine is the submarine itself. Underwater warfare is evidently a disease in which like cures like. In a way this is the most astonishing lesson of the naval operations. It is particularly interesting, because it so completely demolishes all the ideas on this subject with which we entered the war. From that day in history when the submarine made its first appearance, the one quality which seemed to distinguish it from all other kinds of warship was that it could not be used to fight itself. Writers were fond of pointing out that battleship could fight battleship, that cruiser could fight cruiser, that destroyer could fight destroyer, but that submarine could not fight submarine. This supposed quality, which was constantly emphasized, was what seemed to make the introduction of this strange vessel such a dangerous thing for the British Empire. For more than a hundred years the under-water boat was a weapon which was regarded as valuable almost exclusively to the weaker sea powers. In the course of the nineteenth century this engine of sea fighting made many spectacular appearances; and significantly it was always heralded as the one effective way of destroying British domination at sea.