Dönitz was born in Berlin. He entered the Imperial German Navy ("Kaiserliche Marine") in 1911. During World War I, he served on surface ships. Later he was transferred to submarines (U-boats). He remained in the navy after the war and rose through the ranks of the German Navy of the Weimar Republic ("Reichsmarine") and the German Navy of the Third Reich ("Kriegsmarine"). He became a "Großadmiral". He served as Commander of Submarines ("Befehlshaber der Unterseeboote", "B.d.U."). Later, he became Commander-in-Chief of the German Navy ("Oberbefehlshaber der Kriegsmarine"). He got this position, even though he never joined the Nazi Party. Under his command, the U-boat fleet fought the Battle of the Atlantic. He also served as "Reichspräsident" for 23 days after Adolf Hitler's suicide. He ended the war as a prisoner-of-war of the British.