P-61 - 4 cannon plus 4 x 0.5 mg in the turret
Wikipedia on the Corsair
F4U-1C:
The prototype F4U-1C, appeared in August 1943 and was based on an F4U-1. A total of 200 of this variant were built from July to November 1944; all were based on the F4U-1D and were built in parallel with that variant.
[82] Intended for ground-attack as well as fighter missions, the F4U-1C was similar to the F4U-1D but its six machine guns were replaced by four 20 millimeter (0.79 in)
AN/M2 cannons with 231 rounds of ammunition per gun.
[127] The F4U-1C was introduced to combat during 1945, most notably in the Okinawa campaign.
Aviators preferred the standard armament of six .50 in (12.7 mm) machine guns since they were already more than powerful enough to destroy most Japanese aircraft, and had more ammunition and a higher rate of fire.
[128] The weight of the Hispano cannon and their ammunition affected the flight performance, especially its agility, but the aircraft was found to be especially potent in the ground attack role."
All later Corsairs retained the cannon tho' I think