At the start of World War II, he was the senior submarine officer in the "Kriegsmarine", known as "Befehlshaber der Unterseeboote" (BdU). In January 1943, Dönitz achieved the rank of "Großadmiral" (grand admiral) and replaced Grand Admiral Erich Raeder as Commander-in-Chief of the Navy. Dönitz was the main enemy of Allied naval forces in the Battle of the Atlantic. From 1939 to 1943 the U-boats fought effectively but lost the initiative from May 1943. Dönitz ordered his submarines into battle until 1945 to relieve the pressure on other branches of the "Wehrmacht" (armed forces). 648 U-boats were lost—429 with no survivors. Furthermore, of these, 215 were lost on their first patrol. Around 30,000 of the 40,000 men to serve in U-boats perished.