Hi MC202,
>Not quite, what the German study showed was that of B-17's SHOT DOWN, the average of hits needed to do so was 15 to 30. This study did not include B-17's that were damaged but returned to base.
Actually, the German research included anaylsis of the gun camera films and took damaged bomber into account as well as destroyed ones. The conclusion was that 18 hits were necessary to achieve a bomber kill with 50% probability, while 25 hits would yield a 95% probability of kill. (Note it's not linear.)
This is not aircraft-type specific, so expect it to be an average over B-17s and B-24s both. It was common wisdom among Luftwaffe pilots, though, that the B-17 was a lot tougher than the B-24, so the B-17 could be expected to take a few more hits than indicated for the kill.
Regards,
Henning (HoHun)