Dean's "America's Hundred Thousand" states that F4U-4s arrived in Okinawa and went into combat in May, 1945.
Oops, sorrow wrong aircraft. You want the F4U-1A(W) version. Standby.
In January, 1944, some F4U-1As of VF-17 were being re-fitted with water injected engines. VF-17 was in Torokina on Bougainville. January 26, '44, VF-17 was engaged over Rabaul and shot down eight Japanese aircraft. I don't know if the water injected aircraft were involve in this.