Gruppenkommandeur is a Luftwaffe position (not rank), that is the equivalent of a commander of a group or wing in other air forces. Gruppenkommandeur usually has the rank of Oberstleutnant (Lieutenant Colonel), and commands a Gruppe, which is a sub-division of a Geschwader. A Gruppe usually consists of three or four Staffeln, commanded by a Staffelkapitän.
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Gruppenkommandeur Wikipedia(Text) CC BY-SA