Before the outbreak of World War II, individual U-boat flotillas were under the direct command of a single Führer der Unterseeboote (F.d.U.) in the person of Karl Dönitz. who had also acted as commander of the 1st U-boat Flotilla. In 1939, Dönitz's title was renamed as the Befehlshaber der Unterseeboote (B.d.U.) to which all the flotillas directly reported.