There are quite any number of personal histories written by Vietnam helicopter pilots, most quite readable. But, in my opinion there are three which stand out, because they are so well-written. In other words, besides having a great story to tell, the author is a great story-teller.
They are: "Chickenhawk" by Bob Mason, as mentioned; "Maverick" by Dennis Marvicsin, and "CW2" by Layne Heath. The last two authors use a totally different style of writing to Mason, but the results are equally fantastic. Very highly recommended.
BTW, Shwawn's book is outstanding, and for those wishing to delve a little deeper into helicopter aerodynamics without a lot of formulae, W. Wagtendonk's "Principles of Helicopter Flight" is very hard to beat.
Edited for finger trouble.