F4U1c Corsair

The F4U-1C Corsair, featuring four 20mm cannons instead of machine guns, was used by the U.S. Marine Corps primarily during the later stages of World War II, notably seeing action in the Battle of Okinawa. Only 200 were converted from F4U-1A models. They were designed for close air support and intercepted Japanese planes. 
 
Key details regarding the usage of the F4U-1C include:
Combat Role: Used for ground-attack missions and providing close air support.
Armament: Specifically designed with 4 x 20mm cannons for increased lethality.
Theater: Pacific Theater, specifically around Okinawa.
Operator: Primarily U.S. Marine Corps squadrons. 
 
While the F4U-1C specifically had a limited production run, the broader F4U-1 family and later variants were used extensively by the U.S. Navy, U.S. Marines, Royal Navy, and New Zealand Air Force in WWII and the Korean War.