– a Gruppe for maritime reconnaissance. Trägergruppe (TrGr) – (literally "Carrier group"). They consisted of Junkers Ju 87C (Stukas) and Bf 109 T aircraft for the planned German aircraft carrier Graf Zeppelin. It was disbanded in 1940 after the carrier project was scrapped. Rear-area and night attack Gruppen Other types of Gruppe-sized units of various types existed within the Luftwaffe structure as well: Ergänzungsgruppe (ERgGr) – SupplementalGruppen that were attached to a Geschwader for replacing lost aircraft and training. Erprobungsgruppe (ErpGr) – a specialized Gruppe, much like the similar Erprobungskommando (EKdo) units, for field testing new models and on occasions captured Allied aircraft (most notably with KG 200 and the Zirkus Rosarius units respectively), with the ErpGr and EKdo units using a number matching the RLM airframe number of the aircraft design they were meant to test. Nachtschlachtgruppe (NSGr) – a night ground attack group. Predominantly used in anti-personnel and anti-tank roles. Each Gruppe comprised three or four Staffeln, but by late 1944 a fourth Staffel was usually added to fighter units, making the established strength of the unit approximately 65 to 70 aircraft, although during the war years operational strength tended to fluctuate greatly. Personnel strength varied between 35 and 150 aircrew, and 300 to 500 ground personnel. During the mid-war years a fourth Gruppe was introduced in many Geschwader, initially as an operational training unit for new aircrew. However, these Gruppen soon became additional front-line units, performing the same tasks as their sister formations, while new Ergänzungseinheiten, or operational training units, were formed and took up their tasks. Staffel A Staffel usually had nine to 12 aircraft. Others had as few as five or six aircraft due to losses. The commanding officer of a Staffel was known as a Staffelkapitän and had the rank of Hauptmann, Oberleutnant or sometimes Leutnant. Staffeln were numbered consecutively in Arabic numerals within a Geschwader irrespective of the Gruppe they came under. The Staffel designation would be similar to that of the Gruppe except for the Arabic numerals. For example, Staffel 6 of Jagdgeschwader 27 would be designated 6./JG 27. The Staffeln of Gruppe I would be numbered 1, 2 and 3. Those of Gruppe II would be numbered 4, 5 and 6. This was continued for the rest of theGruppen. When a Staffel was transferred from one group to another or from one Geschwader to another, it would be re-numbered accordingly. For