The war at sea began immediately in September 1939 with the Germans sinking merchant ships in the Indian Ocean and the South Atlantic. On 13 December 1939, the Battle of the River Plate in the South Atlantic took place. The German battleship Graf Spee damaged a squadron of British ships off the coast of Uruguay, but in doing so was damaged herself. Hitler ordered her captain, Hans Langsdorff, to scuttle her rather than let her fall into enemy hands. Langsdorff followed his orders and the Graf Spee was sunk. A week later, Langsdorff, draped in the German flag, shot himself.
In his memoirs, Churchill later confessed: ‘The only thing that ever really frightened me during the war was the U-boat peril.’ Britain depended heavily on imports – from iron ore and fuel to almost 70 per cent of all her food. Convoys of merchant ships crossing the Atlantic were escorted by the Royal Navy and, as far as it could reach, the RAF. But there was only so far the planes could travel, leaving a ‘mid-Atlantic gap’, where the convoys were particularly vulnerable to German submarines, or U-boats, which hunted in groups or ‘wolf packs’.
On 9 May 1941, a British destroyer attacked a U-boat, and a boarding party managed to capture the German navy (Kriegsmarine)’s full-scale Enigma coding machine and code books. Although Bletchley Park was already having some success at deciphering the codes, they were now able to do so at will and reroute the convoys in order to avoid the wolf packs. Subsequently, within two months British losses at sea fell by 80 per cent. The discovery helped the Allies throughout the war in all operations.
The champion of U-boats was Commodore Karl Donitz but his superior, Admiral Erich Raeder, advocated the use of large warships. In May 1941, the Kriegsmarine’s greatest warship, the Bismarck, one sixth of a mile long, pitted its strength against the equally impressive HMS Hood, the pride of the British fleet. On the twenty-fourth, exchanging fire from thirteen miles’ distance, the Hood was sunk, losing all but three of its 1,400 crew. The Bismarck had been damaged, but despite leaking oil, managed to escape the British light cruisers following her. But Bletchley Park intercepted the Bismarck’s codes and knew of her destination – Brest, on the western coast of France – where a fleet of British destroyers sought her out and, on 27 May, sunk her. Raeder and his warships fell from Hitler’s favour and it became the turn of Donitz and his U-boats.
The HMS Dorsetshire picking up survivors from the Bismarck, 27 May 1941
From August 1941, British merchant convoys started delivering supplies to the Soviet Union from bases in Scotland and Iceland. A seventeen-day journey, the Arctic Convoys were fraught with danger, not just from the Kriegsmarine and the Luftwaffe, but the treacherous weather and freezing conditions. However, their contribution to the Soviet war effort, which included tanks and guns as well as raw materials, was invaluable in the fight against Hitler.
During 1943, the British managed to breach the ‘mid-Atlantic gap’ with the introduction of ‘Very Long-Range Liberators’ and with Portugal allowing the use of its airbases in the Azores. Once the USA had entered the war, America was launching more ships than the U-boats could sink and destroying more U-boats than Germany could replace. The RAF was by now successfully destroying U-boats with the aid of radar, and bombing shipyards and docks within Germany. With the Enigma decoding technology still playing its part and with three quarters of U-boat crewmen being killed in action, the once menacing U-boat had become an ‘iron coffin’. Although U-boats continued to be employed throughout the war, the ‘Battle of the Atlantic’, as Churchill coined it, had been won. From mid-1943, the Kriegsmarine’s duties were not so much offensive as defensive, protecting their European coasts from the Allied attack they knew, one day, would come.