I once approached this question in a slightly different way, and asked what percentage of the American pilots who actually took off on at least one fighter mission ever scored an aerial victory. I don't remember offhand what the answer was, but it was WAY lower than I initially guessed it to be.Its simply to allow turning the number of USAAF pilots who scored a victory or more, into a percentage of the total pilots who passed through the system who spent at least one part of their operational service flying a fighter in service. An exact answer is not required, but something approximate is useful.