This video is part of a series of 15 animated maps.

View series: The second World War, 1939-1945

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The Battle of the Atlantic

This map is part of a series of 15 animated maps showing the history of The second World War, 1939-1945.

The British economy was heavily dependent on imports for half its food requirements and all of its petrol. It is estimated that, when World War II broke out, there were as many as 2500 ships at sea maintaining the United Kingdom’s trade.

If Germany succeeded in disrupting Britain’s merchant navy, it could prevent the build-up of troops in the British Isles. Thus, the outcome of the Battle of the Atlantic became a major issue in the Second World War.

By summer 1940, Germany controlled much of the European Atlantic coast, and its submarines could easily reach the merchant ships sailing from North America, Gibraltar, and the Cape of Good Hope.  

Its preferred tactic was to attack conveys by night with several submarines grouped together which led to substantial Allied losses.

By the time the United States entered the war in December 1941, German submarines were extending their operations to the eastern seaboard of the American continent, the Caribbean and off the coast of Venezuela.

Throughout 1942, there were heavy losses, and Allied operations were almost totally paralysed.

Nevertheless, the situation improved rapidly:

- The Allies established airbases in strategic areas close to the sea lanes: Iceland, Canada, Brazil and the Azores.  This reduced the “black hole” in the North Atlantic where German U-Boats could avoid attacks from the air.

-Britain’s ability to decode submarine radio communications allowed the Admiralty to have advance information on the movement of U-Boats

-new methods of detection and improvements in weapons made it easier to protect convoys with planes and destroyers.

From mid 1943, German submarines losses increased dramatically, which led to significant reductions in the number of Allied merchant ships lost.

The Battle of the Atlantic continued until the end of the war, but already in 1943, the Allies were able to build more than enough ships to replace those sunk by German submarines.