In the German "Luftwaffe", the principal unit of action was the "Gruppe" (plural "Gruppen"); the equivalent of a French or USAAC/USAAF group. "Gruppen" were part of a "Geschwader" (equivalent to a USAAC/USAAF wing or an RAF group) and the Geschwader were named according to their function. I./StG 77 was "I Gruppe Sturzkampfgeschwader 77", which flew "Junkers Ju 87 Stuka dive bombers". II./JG 26 was "II Gruppe Jagdgeschwader 26", which flew "Messerschmitt Bf 109 fighters", then switched to "Focke-Wulf Fw 190 fighters". Each Gruppe was composed of three, sometimes four, "Staffeln" (singular "Staffel") (usually 8–12 aircraft). Each Geschwader was composed of three Gruppen.