When the soldiers are celebrating in the tent early in the film, they are drinking Budweiser from two-piece stay-tab cans with UPC symbols. Container companies introduced the two-piece can in 1974, the stay-tab in 1975 and the UPC symbol in 1978. Budweiser introduced the can style used in the movie in 1981.
When they board the UH-1 Huey near the church right before the scene where Sgt Elias gets chased, a Philippine Air Force insignia can be seen on the tail boom of the helicopter. The PAF did not operate in Vietnam.
At one point, a character is warned not to drink from a river because he might get malaria. While drinking the water could cause any number of diseases, malaria is not one of them, as it can only be transmitted by insect bite.
When Taylor, King and Crawford are cleaning the latrines, King says he has 39 days left to serve and will be released from duty in March, while Crawford says he has 92 and will be released on April 17th. With 53 days - nearly 8 weeks - separating their discharges and Crawford out on April 17th, King would be out in February, not March.
When the platoon finds the bunker complex, the Lieutenant sends
Taylor and Washington out to guard the flank. Washington has a pack of Marlboros stuck in his helmet. Once he reaches his position, it is a pack of Kools in his helmet.
In the third battle (Ambushed by VC), the machine gunner
(Morehouse) was hit spot on by an artillery shell from friendly fire and was shattered into pieces by the explosion. When the troops evacuated, his quite complete body, although charred, was the first one taken out.
When Bunny is in the tent talking to Junior, he opens his beer can with a "church key" (can opener). But when Lieutenant Wolfe walks in and Bunny bites a piece out of the can, it has a pop-top and shows no sign of having been opened with a "church key".
When Sandy and Sal are investigating the bunker they come across a reused ammo-box filled with maps. The map shown is actually of the British Isles with Ireland, most of England and northern France plainly visible.
A local VC/NVA unit would have no interest in detailed maps of Europe.
In the attack on the camp, we see two NVA/VC soldiers acting as suicide bombers (one falls and explodes, the other makes it into the communication bunker before blowing up). In the script, these two men are identified as sappers. NVA and VC Sappers were specially trained combat engineers/reconnaissance commandos who used stealth to infiltrate a camp's defenses and take out strategic targets, such as barbed wire obstacles or bunkers, with explosives before the main attack. Although there were indeed reports of Viet Cong and North Vietnamese troops using suicide bombers during the war, sappers were never used as suicide bombers because they were considered too valuable to expend.
The uniformed VC/NVA troops are often depicted wearing steel helmets; steel helmets were only worn by NVA anti-aircraft troops protecting base camps in Cambodia, Laos, and North Vietnam. The VC/NVA troops ought to be wearing either floppy "boonie-hats" or the standard NVA sun helmet.
In the opening credits, the military technical advisor Captain Dale Dye is mistakenly credited as belonging to the US Marine "Corp." instead of "Corps". The "US Marine Corps" is a military organization, not a corporation.
Taylor arrives in Vietnam wearing the unit insignia of the 25th Infantry Division. Low-ranking enlisted infantry replacements did not arrive in Vietnam with unit assignments, or insignia, but were assigned to line units as required.
When the booby trapped device (box with Vietcong maps) in the
bunker explodes, it rips off the arms of one of the soldiers. When he stumbles out of the bunker and dies, his hands are clearly visible hanging out under his T-shirt.
During the ambush scene where PVT Gardner shows PVT Taylor a picture of his girl back home, the calendar in his wallet doesn't match 1967. More than likely its a calendar from 1986, the year of production.
When we see Chris and the other new soldiers arriving in Vietnam during the opening sequence of the film they jump to the ground from the rear end of an Air Force C-130 - the rear ramp they would have walked down is missing. The ramp which doubles as the rear cargo door is either closed during long distance flights or partially open flying 'in country' with a rear gunner positioned out on the ramp tethered inside of the plane.
We see a view from the helicopter of Elias running as he gets shot by the Vietcong, and during this shot he raises his arms up, but when it goes to a close up shot of him, his arms are suddenly down and then raised up as he dies.