I believe the F4U-4's where just being accepted/worked up in service during the Iwo Jima battle, Feb.-Mar. 45.
Some early F4U-4 losses in the Atlantic around the same time frame.
80799 (VBF-89) attached to USS Antietam (CV-38) lost in central Atlantic Apr 10, 1945 (BuNos!)
80802 (VBF-89) attached to USS Antietam (CV-38) lost in central Atlantic Mar 25, 1945 (BuNos!)
80805 (VBF-89) attached to USS Antietam (CV-38) lost in central Atlantic Mar 28, 1945 (BuNos!)
If you do a word search for "Iwo" on the above link you will find losses for F4U-1C, -1D & FG-1D airframes during the Iwo battle, but not any F4U-4's.