Having traced the development of submarine warfare to this critical period, we may now turn to the methods and weapons employed by both sides at a time when victory or defeat hinged on the outcome of the war at sea.
Germany's submarine construction and losses appear in the following table from official German sources, the columns showing first the total number built up to the date given, next the total losses to date, and finally the remainder with which Germany started out at the beginning of each year.
After 1916 Germany devoted the facilities of her shipyards entirely to submarine construction, and demoralized the surface fleet to secure personnel. Of the entire number built, not more than a score were over 850 tons. The U C boats were small mine-layers about 160 feet in length, with not more than two weeks' cruising period. The U B'g were of various sizes, mostly small, and some of them were built in sections for transportation by rail. The U boats proper, which constituted the largest and most important class, had a speed of about 16 knots on the surface and 9 knots submerged, and could remain at sea for a period of 5 or 6 weeks, the duration of the cruise depending chiefly upon the supply of torpedoes. In addition there were a half dozen large submarine merchantmen of the type of the Deutschland, which made two voyages to America in 1916; and a similar number of big cruisers of 2000 tons or more were completed in 1918, mounting two 6-inch guns and capable of remaining at sea for several months. The 372 boats built totaled 209,000 tons and had a personnel of over 11,000 officers and men. There were seldom more than 20 or 30 submarines in active operation at one time. One third of the total number were always in port, and the remainder in training.
| Boats built | Losses | Remainder (On Jan. 1 of year following) | |
| End of 1914 | 31 | 5 | 26 |
| 1915 | 93 | 25 | 68 |
| 1916 | 188 | 50 | 138 |
| 1917 | 291 | 122 | 169 |
| 1918 | 372 | 202 | 170 |
It is evident from her limited supply of submarines at the outbreak of war that Germany did not contemplate their use as commerce destroyers. To the Allied navies also, in spite of warnings from a few more far-sighted officers, their use for this purpose came as a complete surprise. New methods had to be devised, new weapons invented, new types of ship built and old ones put to uses for which they were not intended—in short, a whole new system of warfare inaugurated amidst the preoccupations of war. As usual in such circumstances, the navy taking the aggressive with a new weapon gained a temporary ascendancy, until effective counter-measures could be contrived. It is easy to say that all this should have been foreseen and provided for, but it is a question to what extent preparations could profitably have been made before Germany began her campaign. It has already been pointed out in the chapter preceding that, had the German fleet been destroyed at Jutland, subsequent operations on the German coast might have made the submarine campaign impossible, and preparations unnecessary.
Anti-Submarine Tactics
Of the general categories of anti-submarine tactics,—detection, evasion, and destruction—it was naturally those of evasion that were first employed. Among these may be included suspension of sailings upon warning of a submarine in the vicinity, diversion of traffic from customary routes, camouflage, and zigzag courses to prevent the enemy from securing favorable position and aim. The first method was effective only at the expense of a severe reduction of traffic, amounting in the critical months of 1917 to 40 per cent of a total stoppage. The second sometimes actually aided the submarine, for in confined areas such as the Mediterranean it was likely to discover the new route and reap a rich harvest. Camouflage was discarded as of slight value; but shifts of course were employed to advantage by both merchant and naval vessels throughout the war.
Methods of detection depended on both sight and sound. Efficient lookout systems on shipboard, with men assigned to different sectors so as to cover the entire horizon, made it possible frequently to detect a periscope or torpedo wake in time to change course, bring guns to bear, and escape destruction. According to a British Admiralty estimate, in case a submarine were sighted the chances of escape were seven to three, but otherwise only one to four. Aircraft of all kinds proved of great value in detecting the presence of U-boats, as well as in attacking them. Hydrophones and other listening devices, though at first more highly perfected by the enemy, were so developed during the war as to enable patrol vessels to discover the presence and even determine the course and speed of a submerged foe. Along with these devices, a system of information was organized which, drawing information from a wide variety of sources, enabled Allied authorities to trace the cruise of a U-boat, anticipate its arrival in a given locality, and prophesy the duration of its stay.
Among methods of destruction, the mounting of guns on merchantmen was chiefly valuable, as already suggested, because of its effect in forcing submarines to resort to illegal and barbarous methods of warfare. Hitherto, submarines had been accustomed to operate an the surface, board vessels, and sink them by bombs or gunfire. Visit and search, essential in order to avoid injury to neutrals, was now out of the question, for owing to the surface vulnerability of the submarine it might be sent to the bottom by a single well-directed shot. In brief, the guns on the merchant ship kept submarines beneath the surface, forced them to draw upon their limited and costly supply of torpedoes, and hindered them from securing good position and aim for torpedo attack.