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.

In 1940 the Swiss Air Force purchased 12 Me-109 G-6s from Germany and added 2 more captured aircraft. Messerschmitt Bf 109 G6 SAF J-704 Werk Nr 163245 Fliegerkompanie 7, joined the Swiss Air Force on May 26, 1944. The aircraft originally was Stkz RQ-BI. After two engine failure emergency landings, a lost canopy during flight and a crash into other aircraft on the ground. J-704 only had 57 hours flight time so it was repaired, repainted and fitted with a tall tail and withdrawn from service on February 2, 1947.