Atlantic, battle of the, 1939–45. A decisive Second World War battle, the struggle diverged from pre-war expectations. Before the war British naval experts thought ‘Asdic’ countered submarines and, like the highest German authorities, considered surface warships the best means of interrupting transport to Britain of food, munitions, and troops. Hitler allotted priority to submarines only after the fall of France, which gave German submarines greater range from Bay of Biscay harbours. In the first half of 1941 the Germans began to win, using ‘wolf-packs’ of submarines to overwhelm convoys. Ships sunk exceeded new building. In June, however, the British began to decode orders, generated by German ‘Enigma’ machines, giving U-boat assembly areas in the Atlantic. In July 1941, shipping losses from submarine attack fell to less than one-third of those in June in spite of more U-boats. Early in 1942, the Germans recovered; they began to read allied convoy orders and again made their own orders indecipherable. Losses to allied ships exceeded combined British and American building. In 1943, however, at twelve times the volume of 1941, US construction far exceeded losses. Greater numbers and better weapons now gave victory to the British, Canadians, and Americans. ‘Very long-range’ aircraft and small escort aircraft carriers improved allied reconnaissance and attack, as did airborne and shipborne short-wave radar, together with high-frequency direction finding, which enabled warships to locate U-boats as soon as they made radio signals. Depth charges, to destroy submerged U-boats, were improved. The allies won the battle of the Atlantic for good in summer 1943. Victory, first over German surface vessels—most dramatically the defeat of the pocket-battleship Graf Spee in 1939 and of the Bismarck in 1941—and then over German submarines enabled British survival and the build-up of American forces in Britain for the liberation of France in 1944 and the defeat of the Germans in 1945.

R. A. C. Parker