I'm deciphering some of his letters and Tedder seems to sign himself off as "Tirpitz". I can't find any reference to him having done this anywhere else, but these are private letters between himself and C.A.S. Portal. Does anyone happen to know please?
The biographical notes section of Peter Gray's The Leadership, Direction and Legitimacy of the RAF Bomber Offensive from Inception to 1945 mentions that Tedder "Was addressed in demi-official letters as 'Tirpitz'". According to Tedder: Quietly in Command by Vincent Orange it dates back to his days in 25 Squadron in World War I, when a group gave themselves German nicknames (in addition to Tedder as 'Tirpitz' others were 'Bismarck', 'Little Willie' and 'Von Moltke').