Don't confuse War Emergency Power (WEP) with water injection. For U.S. birds, the WEP rating was a higher allowable manifold pressure that carried a time limit, most of the time it was 5 minutes. Most American fighters, regardless of whether or not they had water injection, had a WEP power setting. Water Injection was merely provided to allow higher manifold settings that may or may not have been the WEP power setting. Case in point, the P-47N water injection began at 54" of manifold pressure, even though the WEP rating was 72". Time limit for WEP in the Jug N was 5 minutes continuous, even though it carried 15 minutes worth of water. Conversely, the P-51D had a WEP rating, even though it didn't carry water injection.
So, the F4U-1 may not have had water injection early on, but the R-2800 that powered it did have a WEP rating.
