The Messerschmitt Bf 109 was a single-seat monoplane fighter used by the Luftwaffe before and during WWII. It was used as a fighter, interceptor, high-altitude interceptor, fighter-bomber and reconnaissance aircraft. The Bf 109 F variant, or "Friedrich", was a replacement for the Emil. Friedrich reached front-line units in the Autumn of 1941 and, by the middle of the following year, almost two-thirds of Luftwaffe fighter regiments were equipped with the variant.