Hi Mark,
My point on the 65% losses on aircrew was about the chance of NOT surviving a Tour of Duty (initially 25 missions). The 75% figure on U-boat crew losses, cited often and probably familiar, comes simply from the ratio of those who ever crewed a U-boat and those who were KIA/MIA.
So the American aircrew loss figures that I cited may not be a good comparison because the methodology might not be the same. I found some data on U.S. Army Air Force losses in WWII and they were about 3%, but this is as an organization and not just bomber aircrews, nor exclusive to the European theater.
From my notes on John Keegan--I can get a citation or direct quote the next time I visit a library--I have some figures on RAF Bomber Command, which is an occupation usually acknowledged to have been safer than the American daylight bombings.
The RAF Tour of Duty was 30 missions. Each flyer had the statistical probability of being shot-down before the Tour was completed, which weighed on morale. (That would mean an over 50% chance, I believe.) In 1941, more aircrew were killed than civilians in the raids!
Bomber Harris determined that losses for each mission of up to 5% were acceptable. At Nuremberg on the night of 30 March 1944, the losses were 11%. Morale could not have been lower, but seasoned crews with more than five missions had better odds than novices. With 10% attrition-rates common, crews often bombed short and returned home to base prematurely.
I think that makes my point, although it is not the USAAF figure of 65% Tour-nonsurvival that I used above. I don't recall exactly where I read that but I found it astonishing.
Statistically, if the odds for each mission are 10% then that doesn't mean that you have a 50% chance of being shot-down from five missions. You still have a ten-percent chance each mission. But the overall odds for completing the Tour are bad with even a five-percent chance of getting-it for each of your 30 missions. According to Keegan, it was even-odds or worse for completing a tour with Bomber Command.
Best Regards,
Scott