The post of Führer der Unterseeboote (FdU) ("Type Commander, Submarines") was the senior commanding officer of the submarine service in the Kaiserliche Marine of World War I and the Kriegsmarine of World War II, and the title of several senior commands during the war. From January 1936 and until 17 October 1939, Karl Dönitz served in this position. Thereupon Dönitz was named Befehlshaber der Unterseeboote (BdU) ("Commander of the U-boats"), and two subordinate FdU posts were established, FdU West ("FdU West") and FdU Ost ("FdU East").[1]