Graf, a pre-war football player and glider pilot, he joined the "Luftwaffe" and started flight training in 1936. He was initially selected for transport aviation but was subsequently posted to "Jagdgeschwader" 51 (JG 51—51st Fighter Wing) in May 1939. At the outbreak of war he was stationed on the Franco–German border flying uneventful patrols. He was then posted as a flight instructor stationed in Romania as part of a German military mission training Romanian pilots. Graf flew a few ground support missions in the closing days of the German invasion of Crete.