Any from an aviator's perspective??
It sounds like he would enjoy "B-17s Over Berlin - Personal Stories from the 95th Bomb Group" edited by Ian L Hawkins. You can get a good condition copy or better from Abe Books on line for about $5. There about 75 stories/interviews from the men who flew B-17s. Each story is about 1 to 6 pages long so it can be picked up an read at any time without having to keep track of a plot but I bet he won't be able to put it down.
Cheers!
I remember watching this series with my father when I was a child. Very good. I always remembered the theme music for some reason. There was a monthly magazine of the same name and I still have my 50 year old copies. I purchased the series on DVD 10 years ago. Still very good.Not a book, but the British TV documentary “The World at War” is an oldie but a goldie. Available on Amazon.