Continuity mistake: The day after the USO Playboy Bunny show, the patrol boat canopy is set afire by some pranksters from a passing boat. Yet, that night in the scene at the Do Lung Bridge, the canopy is intact. It goes through some amazing transformations during the remainder of the picture.
Continuity mistake: In the first few scenes with the air cavalry commander, his black hat has a lieutenant colonel rank and a small crossed-sword emblem on it. Later, as his helicopter lands on the beach, his hat has no rank and is emblazoned with a very large crossed-sword Cav emblem.
Revealing mistake: In the major helicopter scene when Ride of the Valkyries is played, the actual tape isn't going over the playing heads.
Continuity mistake: After the helicopter attack when the chopper drops the patrol boat into the water, you can see the canopy and the radar type antenna break and collapse. When you see it again it's in perfect condition.
Factual error: When LtC. Kilgore requests the air strike, you can see that the F-5s are not carrying any ordnance under their wings, except for a centerline fuel tank. Also, their color scheme varies from a white to a greyish one.
Continuity mistake: As Chef grabs the black wig it's clear to see that the window on the helicopter door has a strain crack going down the middle of it. It's there for two shots then when Clean hammers on the helicopter door the first time it's not broken. After he climbs up onto the helicopter and bangs on the front windshield he comes back to the side window a second time and it's cracked again.
Continuity mistake: As they pull up next to the Vietnamese sampan Clean runs to the port side of the boat in order to catch the tow rope. Chef is standing behind Captain Willard in middle of the boat and doesn't move and all. In the next shot Clean and Chef are both standing on the edge of the port side of the boat.
Audio problem: Approaching Kurtz' compound Lance starts drumming on two tin cans and if you listen closely they get the overdub wrong. At first we hear two distinct pitches, which are the actual sounds, picked up by the microphone but the last time he hits it we hear a third higher pitch which was overdubbed. There are only two cans not three and he doesn't change the way he's holding them therefore you can only have a maximum of two audible pitches.
Continuity mistake: Roxanne prepares a pipe for Captain Willard and says, "It was the morphine he took for the wounds he suffered in his heart." The shadow of her left hand falls on her face as she holds the needle over the flame. In the next shot, however, the lighting has changed and the shadow is now nowhere near her face.
Continuity mistake: Colonel Kurtz leaves after he finishes reading the Time articles and there's a close-up of Captain Willard's face and chest. He's soaking wet in the close-up but in the next shot, as he collapses trying to leave the room, his face and chest are dry and there isn't as much dirt on the left side of his chest.
Visible crew/equipment: After Clean is killed there's a shot of Lance sitting on the back of the boat holding a mirror in his right hand. This is not the actor Sam Bottoms but a longer haired thinner stand-in who's not wearing the black wristwatch that Sam wears in every other scene in the movie.
Continuity mistake: As the camera pans along from the rear of the helicopter to the front Chef says to Miss May, "I've got every one of your pictures". Watch very closely as the camera shoots through the two windows on the helicopter's door. The Styrofoam head with the black wig on it that Chef asks the playmate to put on is not up against the left window as it is several shots later inside the helicopter.
Continuity mistake: The old gentleman sitting across the table from Hubert de Marais says, "Maybe in the future we can make something with the Vietminh" and the gentleman to the left of Roxanne replies, "Don't you understand". If you look closely the cigar that he just put into the ashtray in the previous shot, along with its smoke, has disappeared.