The defeat of the U-boat threat was a prerequisite for pushing back the Axis in Western Europe. From 1942 onward, the Axis also sought to prevent the build-up of Allied supplies and equipment in the UK in preparation for the invasion of occupied Europe. Rationing in the United Kingdom was also used with the aim of reducing demand, by reducing wastage and increasing domestic production and equality of distribution. In essence, the Battle of the Atlantic involved a tonnage war the Allied struggle to supply Britain, and the Axis attempt to stem the flow of merchant shipping that enabled Britain to keep fighting. Britain required more than a million tons of imported material per week in order to survive and fight. The Germans were joined by submarines of the Italian Regia Marina (Royal Navy) after Germany's Axis ally Italy entered the war on June 10, 1940.Īs an island country, the United Kingdom was highly dependent on imported goods. These forces were aided by ships and aircraft of the United States beginning September 13, 1941. Convoys, coming mainly from North America and predominantly going to the United Kingdom and the Soviet Union, were protected for the most part by the British and Canadian navies and air forces. The Battle of the Atlantic pitted U-boats and other warships of the German Kriegsmarine (Navy) and aircraft of the Luftwaffe (Air Force) against the Royal Navy, Royal Canadian Navy, United States Navy, and Allied merchant shipping. The campaign peaked from mid-1940 through to the end of 1943.

At its core was the Allied naval blockade of Germany, announced the day after the declaration of war, and Germany's subsequent counter-blockade. The Battle of the Atlantic, the longest continuous military campaign in World War II, ran from 1939 to the defeat of Nazi Germany in 1945, covering a major part of the naval history of World War II.

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