 Following Austria's unification with Nazi Germany in 1938, Bartels was drafted into the Luftwaffe.Bartels' wife's name was Margo, and they had one son, Heinz.Bartels served with the "Ergänzungsstaffel" (Training/Supplement Squadron) of Jagdgeschwader 26 "Schlageter" from the early summer of 1941 onward, claiming his first two aerial victories, two Supermarine Spitfires, on 19 August 1941.