The Befehlshaber der Unterseeboote or BdU (Eng: "Commander of the U-boats") was the supreme commander of the German Navy's U-boat Arm (Ubootwaffe) during the First and Second World Wars. The term also referred to the Command HQ of the U-boat arm. The title was established in June 1917, replacing the role of "Leader of the U-boats" (Führer der Unterseeboote, or FdU) for the High Seas Flotillas. The first incumbent was Kapitan zur See/Kommodore Andreas Michelsen, previously head of the High Seas Fleet’s destroyer force. The post was abolished with the end of the war.