When the war in the Pacific began the Grumman F4F Wildcat was the principal carrier-borne fighter in the US Navy's arsenal and remained so until mid-1943. Originally designed as a biplane, it was redesigned into a mid-wing monoplane in order to remian competitive with its contemporary, the F2A Buffalo, which had originally beaten it for USN orders. The Wildcat had a stubby look, with lapped fuselage panels, a pronounced dorsal spine, and a unique manually-operated main landing gear. Belly windows were also provided for visibility. The Wildcat was powered by Twin Wasp radials and armed with four, later six, .50-in machine guns with provisioning for small bomb loads as well. In combat, the Wildcat was thoroughly outclassed by its main Japanese rival, the A6M Zero, but its ruggedness and pilot skill actually gave it a superior kill rate for air-to-air combat, a testament to its robust design and also to the frailty of its Japanese opponents which lacked armor or self-sealing fuel tanks. Among the Wildcat's battle honors include all the crucial naval battles of 1941-42 like the Coral Sea, Midway and the many engagements around Guadalcanal. Wildcats were also used extensively by the Royal Navy (where they were initially known as the Martlet) and flew with success in the Mediterranean and North Sea from both carriers and land bases. They also became the US's primary escort fighter carrier, operating until the end of the war on small ships which could not carry other larger and heavier fighters. Among its other accomplishments, Wildcats sunk various Japanese submarines and even a cruiser.

The original F4F-1 was conceived as a biplane but never passed the design stage. The first prototype XF4F-2 was first flown on 2 September 1937 but was severely underpowered and incredibly lost out the production contract to the Brewster Buffalo. The prototype was extensively redesigned into the far superior XF4F-3 and was finally accepted into USN service. The initial production variant was the F4F-3 which entered service in late 1940 and was the main Wildcat variant in service when the US entered the war. The similar F4F-3A had less sophisticated R-1830-90 engine due to shortages with the main type. The next main variant was the F4F-4 which was the first to include folding wings for carrier stowage and upped the armament to six machine guns (albeit with the same ammunition capacity, which reduced firing time) in addition to bombs or rockets. In 1942, Wildcat production was taken over by Eastern (General Motors) which produced two versions, the FM-1 (equivalent to the F4F-4 but with only four guns) and the FM-2, designed for service on escort carriers and featuring a more powerful engine, removal of the belly windows, and a noticeably taller tail. Finally a long-range reconnaissance variant was built as the F4F-7. In Royal Navy service, Grumman-produced variants were known as the Martlet, these corresponded as the Mk. I (former French order identified by the company designation G-36A), Mk. II (G-36B), Mk. III (F4F-3A), and Mk. IV (F4F-4). This name was dropped in the later GM-produced variants which were known as the Wildcat Mk. V (FM-1) and Mk. VI (FM-2).