Germans succeeded in maintaining an average of some 40 subma- 

 rines at sea at all times. Allied losses, though far below 

 the April, 1917 ? peak, still averaged approximately 300,000 

 gross tons per montho And U-boat losses were only some 7 per 

 month. 



Of the 178 U-boats sunk during World War I, only 45 per 

 cent were sunk by surface craft. Thirty per cent were sunk by 

 mines, 10 per cent by Allied submarines and the remaining 15 

 per cent were lost through other causes 



It was clear that though the Allies might make the U-boat 

 a weapon hazardous to its user, they still had failed to make 

 its employment a military extravagance. They had yet to de- 

 velop a satisfactory means of detecting and tracking a subma- 

 rine while submerged s and an offensive arm lethal against a 

 U-boat below the surface. 



For anti-submarine ordnance the Allies had the depth 

 charge, but the "ash can" was a crude weapon. It could not be 

 fired forwarded from the pursuing vessel. The depth setting 

 of its fuze was largely a matter of guess work. Large pat- 

 terns of great numbers of charges had to be dropped in order 

 to achieve any chance of a kill. The greatest merit of the 

 depth charge was the damaging effect of its blast on the 

 morale of submarine crews. 



To counter the U-boat menace effectively, some means of 

 underwater detection had to be found and developed,. 



In 1917 the Submarine Signal Company set up a test station 

 and laboratories at Nahant, Massachusetts, to which the Western 

 Electric Company and General Electric Company sent a number of 

 their top ranking scientists to work in a great co-operative 

 endeavor, A few months later the Navy set up the U, S, Naval 

 Experimental Station at New London, Connecticut, This station 

 was staffed with scientists drawn from universities through- 

 out the country. 



Early Listen ing Devices . 



Perhaps the first significant achievement of science in 

 devising counter-measures against the German submarine was the 

 development of devices for picking up and determining the 

 direction of underwater sounds. One method was to use the 

 binaural effect by which in ordinary listening, people determine 



