“Libidinous GIs hardly had to leave the base for their adventures. The swimming pool at Tan Son Nhut, for example, had a reputation as one of the most active gay cruising areas that side of Fire Island. There were usually gay men available for dating among civilian personnel at the USO libraries. For gay soldiers, Sydney became a favorite R and R [rest and recuperation] site–with those cheerful guys who could not seem to get enough of American men. Singapore also featured a rousing gay scene, although this tended to attract more gay Australian and New Zealand soldiers, who were in Vietnam as part of a multinational alliance. The in-country R and R center at Vung Tau was also known for wild gay partying. Discharges on the grounds of homosexuality still occurred in Vietnam, but there was growing tolerance of gay servicemen there, unmatched at stateside duty stations.”
Conduct Unbecoming: Gays & Lesbians in the U.S. Military by Randy Shilts, page 149-150.
See this quote for what life was like in rear areas of Vietnam.