F4U-4: The last variant to be produced during World War II, the F4U-4 began entering service near the end of 1944. It fully equipped naval squadrons four months before the end of hostilities. It had the 2,100 hp (1,600 kW) dual-stage-supercharged -18W engine. When the cylinders were injected with the water/alcohol mixture, power was boosted to 2,450 hp (1,830 kW). The aircraft required an air scoop under the nose and the unarmored wing fuel tanks of 62 gal (234 l) capacities were removed for better maneuverability at the expense of maximum range. The propeller was changed to a four blade type. Maximum speed was increased to 448 miles per hour (721 km/h) and climb rate to over 3,800 ft/min (1,180 m/min) as opposed to the 2,900 ft/min (884 m/min) of the F4U-1A. The service ceiling also increased significantly from 37,000 feet (11,000 m) to 41,000 feet (12,000 m).
The "4-Hog" retained the original armament and had all the external load (i.e., drop tanks, bombs) capabilities of the F4U-1D. The windscreen was now flat bullet-resistant glass to avoid optical warping, a change from the curved Plexiglas windscreens with the internal plate glass of the earlier Corsairs. Vought also tested the two F4U-4Xs (BuNos 49763 and 50301, prototypes for the new R2800) with fixed tiptanks (the Navy showed no interest) and an Aeroproducts six-blade contraprop (not accepted for production).