“Life was much tougher at the front lines, because the field offered so few opportunities for privacy and because the soldiers at the front tended to be younger and less confident in skirting the rules. The Vietnam experience was far less libidinous for the typical gay soldier than was later fantasized in homophile fiction and erotic filmmaking.
Danny Flaherty, for instance, had only one homosexual experience in Vietnam, with his first sergeant’s effeminate driver in the back of a truck. There was, however, a near encounter a few months later, as Danny was smoking pot with a heterosexual sergeant. As Danny took a deep drag of marijuana, he saw that his friend had opened his zipper and was glancing toward him. Danny was extremely stoned; it took a moment to appreciate what was going on. It was a moment too long. The next thing he knew, the zipper was closed. The two of them continued smoking and joking, and neither of them acknowledged that anything out of the ordinary had happened.”
Conduct Unbecoming: Gays & Lesbians in the U.S. Military by Randy Shilts, page 43.
See this quote for what life was like in rear areas of Vietnam.