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The tide turns, 1943-1945

Explosion in sea over a partly submerged submarine

A U-boat is hit by a depth charge from a Fleet Air Arm Avenger aircraft, 1944. Image copyright Imperial War Museum

From mid-1943 the U-boat threat began to recede. At the end of May all U-boats were withdrawn from the North Atlantic for six months. This was to regroup and develop new ships and weapons. Although they remained a threat until the end of the war, the U-boats never regained the upper hand in the Atlantic.

Some of the most important factors in the change of fortune in the Atlantic were:

  • An increased number of British, Canadian and American naval escorts.
  • Convoys now usually had an escort of at least six ships
  • Technological advances such as improved Asdic systems, radar and 'huff duff' (High-Frequency Directional-Finding) equipment. These allowed ships to determine a U-boat's position, bearing and range.
  • From early 1943 Atlantic convoys had better air cover. Naval escort carriers often joined convoys for the entire voyage. Even more crucially, US and Canadian 'Liberator' bombers flying from Iceland and Newfoundland closed the mid-Atlantic 'air gap', which had been such a danger to convoys, by late April. Long range British and American bombers also attacked U-boats near their French bases. More U-boats were sunk by aircraft than by ships during the last two years of the war.
  • Allied success in Europe after the 1944 invasion ended any attempted renewal of the U-boat offensive.