He has been called the "Master Interrogator" of the Luftwaffe, and possibly of all Nazi Germany; he has also been praised for his contribution in shaping U.S. interrogation techniques after the war. As an Obergefreiter (equivalent to Private First Class) he was charged with interrogating captured American fighter pilots after he became an interrogation officer in 1943. He has been highly praised for the success of his techniques, in particular because he never used physical means to obtain the required information.