No F4U-4Bs saw action in WWII. Some photos mislabel F4U-1Cs as F4U-4Bs though and that has caused some confusion.
Adding to the confusion... The F4U-4B designation was originally set aside for F4U-4 deliveries expected to go to the Fleet Air Arm. These were canceled, so the -4B reverted to the Navy. 20mm armed F4U-4s were originally to be designated F4U-4Cs. So yeah, many historians have been baffled by the muddle of designations.
No F4U-4Bs were shipped outside CONUS prior to Japan's surrender.
F4U-4 and F4U-4Bs saw extensive combat duty in the Korean War. Even shot down a MiG-15 and quite a few Yaks.
My regards,
Widewing