The first German mass produced 109 fighter was the Bf-109E that has been mistakenly referred to as the Me-109. The Bf is the designator for the Bayerische Flugzeugwerke (BFW) (Bavarian Aircraft Works) that produced the original aircraft. In 1938 Messerschmitt took over BFW but throughout WWII German handbooks and documents referred to the aircraft as the Bf-109. By the end of 1939 the Bf-109E (Emil) had replaced all other 109 variants and equipped 13 Gruppens with 40 aircraft each. The Bf-109 was the main single-engine aircraft until the Fw-190 came along.
The first Bf-109G “Gustav” entered service in March 1942. New features were a pressurized cockpit with three larger guns mounted on the nose and none on the wings but could be field mounted. The Bf-109G could overheat causing oil leaks; starting a fire forcing the pilot to bail out. The Gustav was produced in many variants including long-range fighters, recon fighters and bomber destroyers. The Bf-109G-6 lacked a pressurized cockpit but was the most numerous Bf-109 produced and the first to carry 13mm machine guns; equivalent to the American 50 caliber Browning.