Promoted to Rear Admiral in 1942, von Friedeburg assumed command of the German U-boat fleet in February of the following year. He was awarded the Ritterkreuz des Kriegsverdienstkreuzes mit Schwertern on 17 January 1945. He succeeded Grand Admiral Karl Dönitz as Commander-in-Chief of the Kriegsmarine when Dönitz became Reich President upon Hitler's suicide (and per Hitler's last will), and was promoted to general admiral on 1 May 1945.