Page:Victory at Sea - William Sowden Sims and Burton J. Hendrick.djvu/159

 chief purpose in writing this book is to describe the activities during the World War of the United States naval forces operating in Europe. Yet it is my intention also to make clear the several ways in which the war against the submarine was won; and in order to do this it will be necessary occasionally to depart from the main subject and to describe certain naval operations of our allies. The most important agency in frustrating the submarine was the convoy system. An examination of the tonnage losses in 1917 and in 1918, however, discloses that this did not entirely prevent the loss of merchant ships. From April, 1917, to November, 1918, the monthly losses dropped from 875,000 to 101,168 tons. This decrease in sinkings enabled the Allies to preserve their communications and so win the war; however, it is evident that these losses, while not necessarily fatal to the Allied cause, still offered a serious impediment to success. It was therefore necessary to supplement the convoy system in all possible ways. Every submarine that could be destroyed, whatever the method of destruction, represented just that much gain to the Allied cause. Every submarine that was sent to the bottom amounted in 1917 to a saving of many thousands of tons per year of the merchant shipping that would have been sunk by the U-boat if left unhindered to pursue its course. Besides escorting merchant ships, therefore, the Allied navies developed several methods of hunting individual submarines; and these methods not only sank a considerable number of U-boats, but played an important part in breaking down the German submarine moral. For the greater part of the war the utmost secrecy was observed regarding these expedients; it was not until the early part