The recall of German U-boat wolfpacks from the central north Atlantic at the end of May 1943 ended the most costly phase of the shipping war for the Allies. Never again would the German U-boats inflict dangerously high shipping losses. The naval war remained bitter, nonetheless, for the U-boats refused to give up, turning instead to new technology and new tactics. Right to the end, they continued to present a plausible threat that caused concern in high Allied circles. Indeed, in January 1945 the First Sea Lord of the Admiralty was moved to warn that, “The high shipping losses which may occur during the first half of 1945 may well prejudice the maintenance of our forces in Europe....”
The ensuing struggle in early 1945 led to a confrontation and tactical changes by the U-boats countered by operational and tactical adaptation produced in reply by Allied anti-submarine warfare (ASW) forces. This last phase of the battle of the Atlantic was fought out for the most part in the confusing and difficult shallow waters around the coasts of the United Kingdom and off the east coast of Canada, moving to the shores of the United States only in the last few months of the war. This campaign provides insights into how new and unexpected initiatives by an enemy could be dealt with even when no technological solutions were readily at hand. It also illustrates the difficulty that both submarine and antisubmarine forces encounter when operating in the challenging environment of shallow water.
McLean, Douglas M. "Confronting Technological and Tactical Change: Allied Anti-Submarine Warfare in the Last Year of the Battle for the Atlantic." Canadian Military History 7, 3 (1998)