Until you have been in a B-17 or similar and seen how small it is, and worn all the kit, and realised how heavy it all is, It's hard to imagine how they did it.
Add to that breathing oxygen for 8 hours, at minus whatever temperature, in a space where you can't stand up straight, then have people shoot at you.....
Then you go home, have a drink with your friends in a local, go to bed in a cold damp hut, and have to do it all again the following day, knowing the rest of your friends never came home yesterday.......
One of the youngest 100th BG airmen, slightly exagerated his age when joining up. He completed his tour of duty by the time of his 17th Birthday!!!!!!!!
Hard to see that happening these days.
Steve