The German Navy (Kriegsmarine) played a major role in the Second World War as control over the commerce routes in the Atlantic was crucial for Germany, Britain and later the Soviet Union. In the Battle of the Atlantic, the initially successful German U-boat fleet arm was eventually defeated due to Allied technological advances like sonar, radar, and the breaking of the Enigma code. Large surface vessels were few in number due to construction limitations by international treaties prior to 1935. The "pocket battleships" Admiral Graf Spee and Admiral Scheer were important as commerce raiders only in the opening year of the war. No aircraft carrier was operational as German leadership lost interest in the Graf Zeppelin which had been launched in 1938. Following the loss of Bismarck in 1941, with Allied air superiority threatening the remaining battlecruisers in French Atlantic harbours, the ships were ordered to go back to German ports.