F4F-3 Wildcat (Martlet Mk.I~III) - with four .50 in (12.7 mm) machine guns (450 round per gun)
F4F-4 Wildcat (Martlet Mk.IV) - entered service in 1941 with six .50 in (12.7 mm) machine guns (240 round per gun) and the Grumman-patented Sto-Wing folding wing system.
FM-1 Wildcat (Martlet Mk.V) - identical to the F4F-4, but reduced the number of guns to four, and added wing racks for two 250 lb (110 kg) bombs or six rockets.
FM-2 Wildcat (Martlet Mk.VI) - optimized for small-carrier operations, with a more powerful engine and a taller tail to cope with the increased torque