 Krupinski entered the "Luftwaffe" in September 1939 as an ensign.From November 1939 to October 1940, Krupinski entered basic air training and, after being assigned as a fighter pilot, the fighter school.Following two weeks of vacation, Krupinski completed his training at "Jagdfliegerschule 5" (5th fighter pilot school) in Wien-Schwechat to which he was posted on 1 July 1940.