Revealing mistakes: The M-16 that Col. Kirby smashes against a tree is a toy gun made by Mattel in the 1960s. You can see tell by the speaker holes in the magazine (which is also much larger than a real M-16 magazine).
Revealing mistakes: Col. Kirby uses a "fatal hookup" when rappelling from the mansion's balcony. He is clearly shown wrapping the rope the wrong way through the karabiner. As soon as weight is put on it, the karabiner opens and the rappeller falls free. U.S. Army karabiners in 1968 were non-locking, and were called "snap links" because of it.
Revealing mistakes: When Kirby's helicopter crashes in a ball of fire the rigging cables used to suspend it are visible.
Revealing mistakes: During the night attack on the base, a medium shot of the attacking "Vietcong" clearly shows that, although dressed in the traditional VC black pajamas and conical straw hats, most, if not all, of them are Caucasians (the film was shot at Fort Benning, Georgia, and many soldiers were hired as extras).
Factual errors: The mortar tube that the crew is using in the pit is a 4.2 inch (diameter) mortar. Yet they are dropping 81mm rounds down the tube. Also, when a round is fired out of a mortar, it sounds like an explosion, not like a small "poof".
Continuity: Before they all leave for Vietnam, Sgt. Muldoon wakes everybody up and turns to Petersen's place and the top of an open guitar case can be seen with a guitar in it. Then we get a look at the place from Muldoon's point of view. The next shot shows Muldoon again, but the guitar is now out of the case and leaning against the wall.
Errors in geography: The movie supposedly takes place in Vietnam. Besides the southern yellow pines that make up 95% of the forests, there is an obvious lack of palm trees and other tropical plants. In addition, in the beginning of the movie they walk past a water tower with a red and white checkered paint scheme. This is how water towers are painted on U.S. military bases in the United States. Forward operation posts do not build water towers like this.
Factual errors: Kirby arrives in Vietnam on an airfield where the airfield operations do not make any sense. For some reason there are troops marching around in circles on the tarmac and one version of every single type of aircraft the army owns sitting right next to each other. In addition, there are jeeps driving all around the tarmac with troops with loaded guns. This is a very dangerous and improbable use of an airfield.
Factual errors: The helicopter Kirby is in does not react correctly in terms of aerodynamics after it is hit and catches fire. The helicopter would have swung violently around, speeded up as it fell, and would have crashed extremely hard, easily killing everyone on board.
Errors made by characters (possibly deliberate errors by the filmmakers): In the opening scene of the film, Sgt. Muldoon states that the founding fathers of the United States began writing the constitution after the revolutionary war was over "from 1776 to 1783". The Revolutionary War in fact ended with the treaty of Paris in November of 1783.
Continuity: In the scene where John Wayne tells Provo to set up a .30 caliber weapon to support the .50 caliber weapon, "Provo" reacts to being shot before the VC actually shoots him.
Revealing mistakes: When the tower that John Wayne is standing on gets hit by enemy fire and begins to fall, the people in the tower shown falling are clearly dummies, not human.
Continuity: In the final scene with Kirby and Hamchuck on the beach, it is clearly around noon or so when the conversation starts, but just a few frames later the sun is setting.
Errors in geography: The famous goof at the end of the movie where the characters watch the sun set over the ocean is impossible as the coast in this section of Vietnam faces East.
Errors made by characters (possibly deliberate errors by the filmmakers): After the Americans arrive at the base camp, John Wayne/Col Kirby introduces David Janssen to the camp commander by pointing his weapon at him and waving it. As a soldier, his character should know better: you treat your weapon as though it is loaded and never point the muzzle at something unless it is a target.
Factual errors: When the AC-47 was firing on the camp, it is impossible for the rounds to strike in a straight line. This is because the aircraft fires while in a bank.
Revealing mistakes: During the rainstorm, it is obvious that characters in the background of the scene are not subject to the rain. The ground in the background is a lighter colour than the ground in the foreground. Also it is apparent that the sun is shining in that area
Continuity: In one of the scenes showing the helicopters leaving the camp, as Tran and Beckworth discuss them it shows a helicopter leaving with the number 4 on it's nose. The scene cuts to Tran and Beckworth discussing two helicopters going on patrol and then cuts back to the helicopter with '4' on its nose taking off again albeit shot from a different angle
Factual errors: One scene shows several helicopters touching down in a landing zone (LZ) near the base camp. Simultaneously (and well before all the helicopters have completed their landing) at least 1 jeep is shown driving out into the LZ, approaching a helicopter from its rear and crowding alongside it's spinning tail rotor. This is extremely dangerous and people have literally lost their heads because of this. Safety mandates that everyone stays clear of all helicopter spinning tail rotors at all times and an LZ should be kept clear of all non-emergency vehicles.
Continuity: At (01:31) A small group of soldiers is gathered with Colonel Kirby (John Wayne) as the "Mike force" is landing in helicopters. Sgt. Provo (Luke Askew) loses his boonie hat as the second chopper in the stick touches down. The cover is seen to fly straight up and is presumably pushed a distance away from the rotor wash. Provo remains without a hat until a closeup scene a few seconds later when he is miraculously wearing it again though he hasn't left the group.
Revealing mistakes: Although hard to spot in the film, still photographs taken on location reveal Colonel Kirby and Captain MacDaniel to be wearing highly polished, standard combat boots - not paratrooper's jump boots - with their tan Class A uniforms in their scenes at Ft. Bragg. Special Forces soldiers, all qualified paratroopers, wore jump boots with both their dress and fatigue uniforms.