I've just taken out 'AIR GUNNER' by Alan W. Cooper, from the library.
Quite a few of these guys were selected from the groundcrew lower ranks and gave a bloody good account of themselves.
One story typifying the harshness of those times is about
the first 1000 bomber raid. Just about anything and anyone was thrown into the pot. A gunnery instructor who was crewed up with a crew that was still in training refused to fly with them because he knew they were not ready for ops. He was immediatly stamped LMF and never seen again.
There are other stories of incredible feats of bravery and sacrifice by these young men.