The British harnessed technological advances and adopted an offensive operational doctrine to reverse the course of the Battle of the Atlantic.
In one of the greatest and longest struggles of World War II, the Atlantic Ocean became the key battlefield as U.S. supplies to further the Allied war effort in Europe were shipped to the United Kingdom and, to a lesser extent, onward to the Soviet Union. By the spring of 1943, the Battle of the Atlantic had reached its dramatic climax: The greatest convoy-versus-U-boat battles occurred in March through May.
March is historically viewed as the high point of German submarines’ execution of a guerre de course; U-boats sank 120 merchant ships (nearly 700,000 tons) with only 15 submarine losses. Moreover, the boats sank nearly two-thirds of the ships (half a million tons) while they were in convoy. Convoy—the bedrock of Allied maritime war strategy—was in question. In retrospect, the British Admiralty noted that “the Germans never came so near to disrupting communication between the New World and the Old as in the first twenty days of March 1943.”