I stand terminalogically corrected! (Is that a word?)
I agree, Lang, and 'When Thunder Rolled' and 'Cheating Death', the latter about air rescue ops in Laos & Vietnam, are certainly 'up there' with the two mentioned.
For a more personal view of the air war over North Vietnam (from Thailand bases), I found the bio of Robin Olds, 'Fighter Pilot' to be outstanding - not that it has anything to do with helicopters, it's just an excellent book about the stresses of flying ops, particularly with the overarching political restrictions imposed from a very safe and remote Washington. It cost the US a lot of pilots & aircraft.
I helped pull a Porter apart once, at Oakey, and stuffed it onto a truck for transport to Canberra. I still marvel at the dexterity of the Porter pilots weaving between the trees during firepower displays at Pucka. Low flying at its most impressive. The closest I got was in a Kiowa and a Blackhawk flying at zero plus a bit (There you are Dave, back to helicopters!)
Mike