As the war raged, Vought continued to experiment with ways to upgrade their potent fighter. One early development, the F4U-2, adapted the F4U-1 as a night-fighter. A number of these aircraft did see service in the war. This was the only night-fighter variant of a naval aircraft to receive an entirely new model type (the F6F-5N was the Hellcat's night-fighter variant of the -5). Another experimental variant, the XF4U-3 looked to improve high-altitude performance with the use of two Bierman superchargers (reliability issues led to the abandonment of the project).
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In 1943 Vought pulled several F4U-1As out of assembly and made further modifications. The most significant was the removal of the six Browning .50cal machine guns and their replacement with four potent Hispano M2 20mm cannon each with 231rds per gun. These explosive shells provided a significant increase in the aircraft's firepower, both due to physical size of the shell and the high-explosive charge in the tip of each round. What would become the F4U-1C was born. Experiments and testing continued to follow throughout 1943 and 1944, with the aircraft being accepted for production.
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Numerous refinements implemented in the F4U-1D, which actually saw deployment to the warzone first, were also adapted into the F4U-1C. The partly-framed canopy of the 1A was replaced with the full bubble used in the 1D. Parts of the fabric undersides of the wings were replaced with metal plates, the centerline pylon was omitted and replaced with the same two inner-wing pylons as the 1D, and rocket stubs were added for two 5" HVAR rockets on each wing for a total of four. The fuel tanks in the wings were also omitted. The 1C also utilized the same landing gear oleo strut corrections that would finally make the F4U fully carrier-qualified.
Despite the remarkable power of the 20mm cannon the weapons were not well-received. The US-built version of the Hispano 20mm was notoriously unreliable. Additionally, some early 1Cs suffered from gun jams at higher altitudes until improved deicers for the guns could be installed. Changes made for the M2 version were insufficient to rectify all the problems, however when it worked the Hispano was a powerful weapons system and gave the 1C a massive punch that made her superb as a strike aircraft due to the effectiveness of the 20mm against more hardened targets on the ground. In the air the general fragility of the Corsair's Japanese opponents made the increased power of the 20mm unnecessary, and most pilots preferred the more reliable and still potent Browning .50cal due to its higher rate of fire and larger ammunition load. The increased mass of the cannon and its ammunition also impacted performance, and the 1C was the least maneuverable of the main Corsair variants.
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In addition to its armament, another peculiarity of the 1C is the BuNo series. F4U-1C airframes were pulled from random blocks off assembly lines for the F4U-1A, so there is little direct progression in the serial numbers of the 1C. Only one F4U-1C, the first test mule designated #277, was painted in the tricolor scheme. The rest were all painted in the same semi-gloss sea blue as the 1D.
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Unit Deployment
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The F4U-1C was one of the rarest Corsair variants produced. Only 200 were built, in part due to the preference for the Browning .50cal. Despite entering development and production first, the 1C actually entered active service after the 1D. The first 1Ds began to arrive in 1944, but the 1C was not deployed to the Pacific until the Spring of 1945. F4U-1Cs were flown by a small number of units in the Pacific, including VF-85 off USS Shangri-La. Interestingly, VF-85 shared their home base with the F4U-1Ds of VBF-85. Both squadrons actually operated interchangeably, with both men and aircraft shuffling between squadrons as need or availability dictated. Carrier Air Group 85 is perhaps unique in the Navy of fielding two F4U squadrons and no F6Fs, (although six were carried for night-fighter and reconnaissance duties) and was certainly unusual for operating one with the rare 1Cs, and the other the more conventional 1Ds.
F4U-1Cs in small numbers flew combat sorties throughout the final months of the war alongside the F4U-1D, and soon the last Corsair variant to see action in WWII and the aircraft that could be the greatest American fighter of the Second World War: The F4U-4.