F4U-1D in the Vought Plant
Squadrons in the Pacific that provided ground support carried out various field modifications on the Corsair to allow it to carry heavy munitions. These alterations were mostly improvised and based on individual preference. The F4U-1C, equipped with cannons for ground strafing, did not produce the expected results. As a result, Vought addressed the issue with the next variant, the F4U-1D. The -1D was an improved version of the late production F4U-1A and was introduced in April 1944 while the -1C was still in production. The armament was changed from a four-cannon arrangement to six Browning 0.5-inch (12.7 mm) machine guns. Additionally, hardpoints were added under the wing centre section to carry two bombs weighing up to 1,000 lb (454 kg). These bombs were quite powerful, equaling or even exceeding the bomb load of several types of twin-engined light bombers. The pylons were “wet,” meaning they contained fuel lines in case fuel drop tanks needed to be hung in place of bombs. In that case, two 160 US gallon (606 L) fuel drop tanks were carried. The outer wing panels were fitted with Mk 41-2 racks to lift two 100 lb (45 kg) bombs, but in the last 266 examples of the 1Ds, these were substituted for more effective 5-inch (127 mm) HVARs (High Velocity Air Rockets) on zero-length launchers, with four being fitted under each outer wing. The rockets were sighted via the machine gun sight and proved to be accurate. A number of earlier -1Ds were retrofitted with the rocket installation. The unprotected leading edge wing fuel tanks inherited from the F4U-1A were eliminated. The R-2800-8W engine provided power through methanol/water injection. From BuNo 57356 onwards, the 1Ds were equipped with a smaller propeller of 13 ft 1 in (3.99 m) diameter. The maximum take-off weight increased to 13,120 lb (5,957 kg), but performance remained impressive at 425 mph (684 km/h) at 20,000 ft (6,095 m), although it dropped to 328 mph (528 km/h) at sea level. With drop tanks, the F4U-1D had a range of 1,562 miles (2,514 km), while it could climb at an initial rate of 3,120 ft/min (951 m/min) up to a ceiling of 37,000 ft (11,280 m). Vought built a total of 1,685 F4U-1Ds, with similar models being produced by Goodyear, which manufactured no less than 2,019 FG-1Ds, and Brewster’s 179 F3A-1Ds, which was the last variant constructed by the ill-fated company before its demise. The -1D was an important variant, as it was not only the first real ground support Corsair but also its definitive wartime variant. The first F4U-1D to roll off the Vought assembly line in April 1944 was BuNo 50350 and was accepted by the US Navy on the 22nd of that month. It took part in combat operations that same summer during the advance through the Marshall Islands. In April of that year, the F4U-1D became the first variant of the Corsair approved for US aircraft carrier service, two full years after the first was delivered to the US Navy. This became possible after 113 trial landings by training squadron VF-301 on USS Gambier Bay were successfully.