I have been looking into the attack on the train carrying Fi 103s on September 1 1944 and discussing it on RAFCommands forum. Here is what I have just posted there:
I found the confirmation needed: it was American 8th AF escorts released from their mission when the bombers were scrubbed on September 1 1944. The document doesn't name individual squadrons but there were 47 P-38s and 496 P-51s on escort duty that day. The summary of activity says that 'one group strafed and damaged one locomotive' and ground witnesses reports would make that the P-38s.
Claims for fighters on that day, including those released from escort duties, include:
' Ammo or Buzz Bomb freight cars - 44 destroyed, 15 damaged '
Interestingly, the document quoted was dated 2 September so the description of 'Buzz Bomb freight cars' was included less than 24 hours after the action: sounds like somebody had a good source of information!
Hope this helps tie up a loose end or two.
Bruce