The last major wartime production variant of the Corsair was the "F4U-4", which featured a P&W R-2800-18W Double Wasp with 1,567 kW (2,100 HP) takeoff power and water-methanol injection. The only visible differences from the F4U-1D were an inlet fitted in the lower lip of the cowling, giving the aircraft's nose a slightly different profile, and a four-bladed propeller was fitted. All following Corsair variants would retain the four-bladed propeller. The F4U-4's engine and propeller gave it a top speed of 718 KPH (446 MPH), about 48 KPH (30 MPH) faster than the F4U-1D. Armament was the same as for the F4U-1D, with six Brownings, stub pylons for eight HVARs, and the ability to carry two 450 kilogram (1,000 pound) bombs and a centerline drop tank.
In October 1944 the new factory instructions for the F4U production called for application of Interior Green on all internal surfaces including the cockpit. As an anti-glare measure, all cockpit panels above the lower edge of the instrument panel were to be painted matt black. Curiously, the new directive did not explicitly state what was to happen with the cowling's inner surface. Thus, subsequent machines showed either Zinc Chromate or Interior Green cowlings, until the last standardisation of colour post-war whereupon black was introduced in this area.
During that period, the wheel wells were also painted Interior Green. Undercarriage legs were initially still finished in light grey, but as existing stocks of parts were used up at the factory, the overall Glossy Sea Blue finish was carried over to the undercarriage legs and wheel hubs.