James Webb provided the story for the film, based partly on his own military experience in Vietnam and his tenure as the Secretary of the Navy under President Ronald Reagan; in 2006, Webb was elected as Virginia's newest U.S. Senator.
At the beginning of the movie, some Colt M16 VNs can be seen handled by the platoon of soldiers, a few M60 machine guns, a Remington 870 Combat Shotgun, a couple of RPD Machine guns and some AK-47s in the hands of the Vietcong. Later on, the Marines arriving at the Embassy scene carried M16A2s, some carried Minimi M249 Machine Guns, and the Embassy Guards carried Mosberg Shotguns (unsure of the exact type), while the Yemenese carried AKs and SVD Dragunovs and various small arms.
The trivia item below may give away important plot points.
The scene of Sokal viewing and destroying the tape after he sees it proves gunfire was coming from the crowd, was imposed by test audiences according to William Friedkin. The film was supposed to leave ambiguous whether or not Childers did the right thing, depicting what happened through subjective viewpoints and never revealing the objective truth of what occurred.