 After the surrender he was delivered by US military to the Soviet authorities and remained in captivity until 1949.Post-war, his military service in the "Bundeswehr" saw him promoted to "Oberstleutnant".Gratz served in "Jagdbombergeschwader" 33 (JaBoG 33—Fighter-Bomber Wing 33) flying the Republic F-84F Thunderstreak then under the command of Walter Krupinski.