How many changes did the F4U-1 undergo during production?

Production F4U-1s incorporated several major modifications compared to the XF4U-1. Armament changed to six wing-mounted 12.7 mm (.50 in) M2 Browning machine guns, three in each outer panel, with 400 rounds for the inner pair and 375 for the outer, which forced the wing fuel tanks to be relocated. A self-sealing 897 L (237 US gal) tank took the place of the fuselage armament, so the cockpit had to be moved back 810 mm (32 in) and the fuselage lengthened. 68 kg (150 lb) of armor plate were added, along with a 38 mm (1.5 in) bulletproof windscreen mounted internally, behind the curved Plexiglas windshield. The chosen engine was the more powerful R-2800-8 (B series) Double Wasp, rated at 2,000 hp (1,500 kW).

On the wings, the flaps became NACA slotted type, and the ailerons gained span to increase roll rate, which reduced the flap span accordingly. IFF transponder equipment was fitted in the rear fuselage. All these modifications together increased the Corsair's weight by several hundred pounds.

In total, seven major changes were introduced to the F4U over the course of a year and a half, each requiring considerable research, engineering and testing work. The fifth production aircraft was modified to raise the pilot's seat, a development that led to the clear, frameless "bubble" canopy. Another change consisted of adding a small spoiler on the leading edge of the starboard wing to reduce accelerated stalls and ensure stall warning.