fighting pair also added to its flexibility, as a Schwarm could easily break into two Rotte pairs without losing its fighting ability. The Rottenführer could attack enemy aircraft, leaving his wingman to watch for the enemy. It was much more flexible than the rigid three-aircraft "Vic" formation the RAF used at the start of the war. In the Schwarm the aircraft had plenty of space to maneuver, so they were free to scan the horizon for enemy aircraft rather than focusing on maintaining a close formation. This flexibility became apparent to the RAF during the Battle of Britain. Ground combat forces Anti-aircraft units Luftwaffe controlled the bulk of German anti-aircraft artillery (commonly called Flak) since the 1930s. The smallest tactical unit of anti-aircraft artillery was a battery (). Battery usually had four to six guns. The larger unit was a battalion (Flak-Abteilung), composed of three to five gun batteries and a searchlight battery. Battalions would be "light" (leichte), "mixed" (gemischte), or "heavy" (schwere), referring to the size of guns in their batteries. Flak guns in use were in two light calibers and three heavy calibers – light 20 mm and 37 mm; and the heavy 88 mm, 105 mm, and 128 mm. The battalions were variously organized into regiments (Flak-Regimenter), brigades (Flak-Brigaden e.g. Flak-Brigade XIX), divisions (Flak-Divisionen, e.g. 27. Flak-Division) and flak corps (Flakkorps), although the hierarchy was neither very strict or very stable throughout the history. Over the course of the war, the continuous attacks by first RAF, then USAAF bombers on German cities led to increases in the number of flak units deployed in Germany. Late in the war, AA units were bolstered by the use of foreigners and German youths. There were a total of 29 flak divisions. Each division generally consisted of five flak regiments, one searchlight regiment, three motorized flak transport battalions, one communications battalion, and supply troops. The number of transport battalions varied depending on location and need of transport of the divisions. The first of these was formed in Berlin on 1 July 1938 as the Air Defense Command (Luftverteidigungskommando) but later renamed as 1st. Flak Division. Paratroops One of the unique characteristics of the Luftwaffe (as opposed to independent air forces of other nations), was the possession of an organic paratrooper force; the Fallschirmjäger. These were established in 1938. They saw action in their proper role during 1940–1941, most notably in the