Atlantic, Battle of the

In World War II, contest between Great Britain (and from December 1941 the United States) and Germany for the control of Atlantic sea routes. For the Allied Powers, the battle had three objectives: blockade of the Axis Powers in Europe, security of Allied sea movements, and the freedom to project military power across the seas. The Axis, in turn, hoped to frustrate the Allied imperative of moving men and equipment across the oceans. For British Prime Minister Winston Churchill, the Battle of the Atlantic represented Germany's best chance to defeat the Western Powers.

The first phase of the battle for the Atlantic lasted from the autumn of 1939 until the fall of France in June 1940. During this period, the Anglo-French coalition drove German merchant shipping from the Atlantic and maintained a fairly effective long-range blockade. The battle took a radically different turn following the Axis conquest of the Low Countries, the fall of France, and Italy's entry into the war on the Axis side in May–June 1940. Britain lost French naval support at the very moment when its own sea power was seriously crippled by losses incurred in the retreat from Norway and the evacuation from Dunkirk. The sea and air power of Italy, reinforced by German units, imperiled and eventually barred the direct route through the Mediterranean Sea to the Suez Canal, forcing British shipping to use the long alternative route around the Cape of Good Hope. This cut the total cargo-carrying capacity of the British merchant marine almost in half at the very moment when German acquisition of naval and air bases on the English Channel and on the west coast of France foreshadowed more destructive attacks on shipping in northern waters.

At this critical juncture, the United States, though still technically a nonbelligerent, assumed a more active role in the battle for the Atlantic. Through the provisions of the Lend-Lease Act, the United States turned over 50 World War I destroyers to Great Britain, which helped to make good previous naval losses. In return, the United States received 99-year leases for ship and airplane bases in Newfoundland, Bermuda, and numerous points in the Caribbean. U.S. units were also deployed in Iceland and Greenland.

Early in 1942, after the United States had become a full belligerent, the Axis opened a large-scale submarine offensive against coastal shipping in American waters. German U-boats (submarines) also operated in considerable force along the south Atlantic ship lanes to India and the Middle East. The Allied campaign (1942–43) to reopen the Mediterranean depended almost entirely upon seaborne supply shipped through submarine-infested waters. Allied convoys approaching the British Isles, as well as those bound for the Russian ports of Murmansk and Archangelsk, had to battle their way through savage air and undersea attacks. It was publicly estimated at the close of 1942 that Allied shipping losses, chiefly from planes and U-boats, exceeded those suffered during the worst period of 1917 during World War I. And a considerable weight of Allied naval power had to be kept constantly available in northern waters in case Germany's formidable surface raiders, especially the super battleship Tirpitz, should break into the Atlantic shipping lanes as the Bismarck had done briefly in 1941.

In 1942 and early 1943 the ever-tightening Allied blockade of Axis Europe began to show perceptible progress in combating the Axis war on shipping. With more and better equipment, the convoy system was strengthened and extended. Unprecedented shipbuilding, especially in the United States, caught up and began to forge ahead of losses, though the latter still remained dangerously high. Bombing raids on Axis ports and industrial centres progressively impaired Germany's capacity to build and service submarines and aircraft. The occupation of virtually all West African ports, including the French naval bases at Casablanca and Dakar, denied to Axis raiders their last possible havens in southern waters. By these and other means, the Atlantic Allies thwarted Axis efforts to halt the passage of American armies and material to Europe and North Africa, to prevent supplies reaching Britain and the Soviet Union, and to break up the blockade of Axis Europe.

The battle's decisive stage was early 1943, when the Allies gained a mastery over Germany's submarines that translated into significant reductions in shipping losses. By the time of the Normandy Invasion in June 1944, the Battle of the Atlantic was essentially over, and the Western Powers exercised control of Atlantic sea-lanes. Though German U-boats continued to operate in the Atlantic almost until the end of the war, they were ineffective against Allied convoys and were systematically sunk almost as fast as they made it out to sea.

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