The helicopter delivering supplies to the firebase constantly fires rockets at the enemy, but no rocket pods are visible.
The Huey that first landed at Firebase Gloria had wire cutters installed [which is an anachronism] but when it landed in the rear so the pilot could get supplies, there was no wire cutter on that Huey. Different Huey.
Tan Son Nhut Airbase goes from being heavily fogged in to completely clear in a split second.
The "air cavalry" pilot consistently has his helmet microphone several inches away from his mouth. Because of the noise levels in Hueys, pilots kept their microphones touching their upper lip for best results.
When the Huey lands at the rear base after dropping off supplies the first time, the cargo doors have full length window panels; the actual cargo doors have half-panels.
30 round magazines are used in the M16s they would have been using 20 round magazines.
Huey pilots sit in the left seat co-pilots the right so Maron was in the wrong seat.
During one of the early battles, Haffner throws a hand grenade at one of the towers shielding several attacking Vietcong. The dummy hand grenade bounces back off one of the posts and is still bouncing around in the foreground when an explosion goes off anyway behind the tower.
Capt. A.J. "Bugs" Moran shouts "You picked a fine time to leave me, Lucille" obviously referencing the song recorded by Kenny Rogers in 1977--two years after the fall of Saigon and the end of the war.
The Texas license plates hanging in the command bunker were not issued until 1975.
Poster on the bunker wall says, "Give Peace a Chance". John Lennon didn't record this song until July 1969, almost a year and a half after the Tet Offensive.
Many of the Hueys shown have wire cutters (sometimes called "swords") installed (angled cutters on top and bottom of the airframe above the pilots), which were not in use in 1968. They became standard in the 1970s.
The movie takes place during the Tet Offensive in January 1968. The centerfold the commanding officer shows in the bunker is Cynthia Myers, Miss December 1968.
Boom mic shadow visible during the last scene in which Haffner and the rest of the Americans pursue the attacking Vietcong out of the Firebase.
Flanagan tells the doctor that his M-16 has a full clip. Civilians use that terminology. Marines refer to them as magazines.
Captain Williams refers to Sergeant Major Hafner and Corporal DiNardo as "soldier". No Marine would call another Marine a soldier nor would any Marine allow him/herself to be referred to as a soldier.