Submarine Merchantmen. — The first (and possibly the last) submarine merchantman was the "Deutschland," which crossed the Atlantic with a valu able cargo of dyestuffs from Germany and reached the United States in July, 1916. She is believed to have had a sister ship known as the "Bremen," and this is supposed to have been captured or sunk by the British. The utility of the submarine for carrying cargo is ob viously small. Its comparatively slow speed, its high cost of construction, its small capacity and its general incon venience, render it not worth considera tion as a cargo carrier. It is inconceiv able that it will ever be used as such 'in the future, except by a country which finds itself situated as Germany was in the late war, with its main fleet impotent and its mercantile vessels swept from the seas.
Previous to the European War there were many to be found, even among the highest authorities, who prophesied that the submarine had rendered the surface war vessel useless and impotent. In the early months of the war, when German submarines scored heavily against Brit ish and French cruisers, it seemed as though their prophecies were to be ful filled. As the power of the submarine grew, however, the means of fighting it grew more rapidly, and in the later years of the war almost its only success was against the unarmed or lightly armed merchantman. Deadly though it may be, the submarine, by its very nature, is vul nerable. Many methods of destroying it
were devised, some of which have become known, while others still remain secret. One of the earliest schemes was the con struction of huge nets, two lines of which were placed across the Straits of Dover, from the coast of England to the coast of France, thus providing a compara tively safe space between the two lines. The construction of the vast mine fields in the North Sea has already been dealt with in the early part of this article. Another device that was perhaps more dreaded by the submarine than any other was the "depth charge." This was a huge bomb, weighing 600 pounds or more. One or more of these bombs would be dropped from the stern of a destroyer where a submarine was last seen to sub merge. They would explode at or near the bottom, and the enormous concussion would bring about the complete destruc tion of the submarine. The hydrophone was another useful device invented dur ing the war. This was a special type of telephone, by means of which the posi tion of submarines could be detected by noises transmitted through water. These, and other devices, have greatly lessened the deadliness of submarines in legiti mate warfare. None the less, they are still recognized as a powerful weapon of both defense and offense, and form an important adjunct to all modern navies.