Commissioned into the German Navy as an officer in 1910 Doenitz was Flag Officer U-Boats until 30 January 1943. Convinced that the U-Boat alone could win the war for Germany, he was in fact almost proved correct: he was responsible for sinking fifteen million tons of Allied shipping. By early 1943 he had more than 200 U-Boats operating in ‘wolf packs’ and 181 in production. However the development of radar made the discovering and destruction of U-Boats easier and the Western Allies had closed the ‘air gap’ in the central Atlantic by 1943. These two facts meant that the Allies began to win the convoy battle. Doenitz was promoted to command the German Navy replacing RAEDER. Although the German Navy was now in decline, Doenitz never lost the admiration and respect of HITLER, perhaps because the Navy alone remained loyal. Leaders in the Army had proved themselves treacherous and the Reich Marshal of the Luftwaffe incompetent. Hitler chose to name Doenitz as his successor and Head of State. Doenitz assumed the leadership on 30 April 1945 and negotiated the capitulation of the German forces in the west. He was imprisoned at Flensburg until he was tried at Nuremberg where he was sentenced to ten years for war crimes.