Writer William L. Nagle was an Australian S.A.S. soldier who served tours of Vietnam between 1965 and 1969.
R. Lee Ermey, who plays Sgt. Maj. Hafner, really is a former US Marine and veteran of the Vietnam War.
Shot in an area of the Philippines undergoing a Communist rebellion, and both sides of the conflict actually contributed to the film's production--the Communist guerrillas of the New People's Army were hired as security guards, and the Filipino government supplied the helicopters and pilots, which sometimes came to the set right after they finished attacking Communist positions.
The "Playboy" Playmate shown by CO Williams is December 1968 "Playmate of the Month" Cynthia Myers. NOTE: She was only 17 at the time the photos were taken, but the magazine waited until she was 18 to publish them.
Brian Trenchard-Smith has stated that the film was intended to focus on war and reconciliation, and the final scene would have featured R. Lee Ermey recognizing the Viet Cong colonel he fought (played by Robert Arevalo) years after the end of the war and warmly greeting him in Vietnamese. However, this and other scenes furthering the theme of reconciliation were cut prior to sound mixing at the behest of the American producers, who thought that a focus on the Vietnamese point of view would alienate American audiences.