Atlantic Warfare Today : 425 



could be an easy target for the submarines, the merchant ships 

 would be too slow and they would fail to follow prescribed courses, 

 etc. A trial convoy of eight-knot merchantmen was finally assembled 

 at Gibraltar and, under destroyer protection, made the passage to 

 England with perfect operation and without loss of a vessel. 



Other defenses against the submarine developed rapidly. The 

 "depth charge" demonstrated its value and came into wider and 

 more effective use. In essence, the depth charge was simply a large 

 steel drum filled with high explosives. This was detonated by a de- 

 vice set to go off at a predetermined pressure and therefore, of course, 

 at a predetermined depth. A considerable number of depth charges 

 were mounted at the stern of destroyers and other vessels and simply 

 plopped overboard by a light explosive charge. The depth charge 

 was not a missile and it was not necessary for it to hit a submarine 

 in order to be effective. It was only necessary for the depth charge to 

 explode in the water in the vicinity of the submarine in order to set 

 up a shock wave sufficient to damage the plates of the underwater 

 craft. 



A number of other developments came along to make the use of 

 the depth charge more effective and to build up a submarine defense 

 complex. These elements included an increased use of destroyers for 

 escort purposes, the use of large numbers of small high-speed anti- 

 submarine vessels, the development and use of improved listening 

 devices for detecting the noise of a submarine and therefore its loca- 

 tion, the use of seaplanes and other aircraft for spotting submarines 

 by air — radio being employed for contact between the aircraft and 

 the antisubmarine surface vessel. Thus, for example, a seaplane and 

 a number of antisubmarine vessels would jointly be assigned for the 

 protection of a particular area of the ocean or coastline. When the 

 airplane on patrol sighted a submarine it would use the radio to in- 

 form one or more of the antisubmarine boats as to the exact location 

 and estimated depth of the submarine. The high-speed surface craft 

 would then converge on this point and drop their depth charges or 

 otherwise attack the vessel. 



The Germans expected and the Allies feared that during the days 

 of long sunshine which mark the spring in northern waters the sub- 

 marines would sight their targets for many more hours and that con- 

 sequently in May and June and the later summer months the toll of 

 submarine sinkings would rise. Actually nothing of this kind hap- 

 pened even though the number of German submarines increased to 



