From the F-4 onward, the new 20 mm Mauser MG 151/20 with 200 rounds was used as the Motorkanone. The first F-4s reached frontline units in June 1941. Production lasted exactly a year between May 1941 and May 1942, with 1,841 of all F-4 variants produced. Some of the later models were capable of mounting two 20 mm MG 151/20 cannons under the wing in faired gondolas with 135 rpg. These were designated F-4/R1 and 240 of them were produced by WNF in the first quarter of 1942. This optional additional armament was standardized as field kit for later G and K series. A special high-altitude variant, the F-4/Z featuring GM-1 boost, was also built with a production run of 544 in the first quarter of 1942 and saw extensive use. Finally, the Erla factory produced 576 tropicalized F-4 trop in the first half of 1942.
With its initial engine rating of 1,200 PS, the maximum speed of the F-4 (and F-3) was 635 km/h (394 mph) at rated altitude; and with the clearance of the full rating of 1,350 PS, maximum speed increased to 659 km/h (410 mph) at 6,200 m (20,341 ft)