F4U-4: The last variant to see action during World War II. Deliveries to the U.S. Navy of the F4U-4 began in early 1945. It had the dual-stage-supercharged -18W engine. When the cylinders were injected with the water/alcohol mixture, power was boosted to . The aircraft required an air scoop under the nose and the unarmored wing fuel tanks of 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 and climb rate to over as opposed to the of the F4U-1A. 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 distortion, 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 wingtip tanks (the Navy showed no interest) and an Aeroproducts six-blade contraprop (not accepted for production).