Karl Dönitz (16 September 1891 – 24 December 1980) was a German naval commander during World War II. He started his career in the German Navy (Kaiserliche Marine, or "Imperial Navy") before World War I. In 1918, while he was in command of UB-68, the submarine was sunk by British forces and Dönitz was taken prisoner. While in a prisoner of war camp, he formulated what he later called Rudeltaktik ("pack tactic", commonly called "wolfpack"). At the start of World War II, he was the senior submarine officer in the German Navy. In January 1943, Dönitz achieved the rank of Großadmiral (Grand Admiral) and replaced Grand Admiral Erich Raeder as Commander-in-Chief of the German Navy (Oberbefehlshaber der Kriegsmarine). On 30 April 1945, after the death of Adolf Hitler and in accordance with Hitler's last will and testament, Dönitz was named Hitler's successor as Staatsoberhaupt (Head of State), with the title of Reichspräsident (President) and Supreme Commander of the Armed Forces. On 7 May 1945, he ordered Alfred Jodl to sign the German instruments of surrender in Rheims, France. Dönitz remained as head of the Flensburg Government, as it became known, until it was dissolved by the Allied powers on 23 May.