Führer der Unterseeboote
The post of Führer der Unterseeboote was the senior commanding officer of U-boat forces in a theatre of war. The submarine service in the Kaiserliche Marine of World War I and the Kriegsmarine of World War II, used the title for several senior commands during those conflicts. It was senior to Flotilla chief and was introduced as U-boat forces in an area expanded beyond flotilla size. In 1917 the posts of FdU were themselves subordinated to an overall "Commander of the U-boats". The post of FdU was revived in the 1930s with German re-armament and was held from January 1936 and until 17 October 1939 by Karl Dönitz. On that date he was named BdU, and two subordinate FdU posts were established, FdU West and FdU Ost.
In the further course of the war, several further posts were created for the commanders of U-boat regions