Continuity mistake: Dennis Hopper walks to the back of the boat and says, "I'll tell you one thing. This boat is a mess man, whoo!" As he stands in the middle of the boat note the machine guns are missing, yet in the following shot they reappear with their ammo. Later, as he moves back to the front of the boat the disappear yet again. (02:30:10)
Continuity mistake: As they approach Vin Din Dop in Lieutenant Colonel Kilgore's helicopter there's a close-up of Captain Willard looking out of the helicopter. If you look closely there's no wind because the helicopter is not flying. In the next shot as Colonel Kilgore talks to Lance about surfing, it is and there's plenty of wind. (00:36:15)
Continuity mistake: Captain Willard reads on uninterrupted from "Commitment and Counterinsurgency" by Colonel Kurtz who says in his report, "if they were committed this war can be won with a fourth of our present force". The weather changes from not raining to raining, back to not raining again between shots. (01:15:40)
Other mistake: As the woman that threw the grenade into the Medevac helicopter runs away they shoot at her from another helicopter. You can see by the puffs of smoke on the ground that the machine gun fire is not going anywhere near her, or her friend running in front of her as they fall to the ground dead. (00:44:30)
Continuity mistake: As Colonel Kilgore calls out to the soldiers surfing in the water Captain Willard's band-aid on his right cheek appears out of nowhere for the first time in the movie. He had no band-aid on his face before this and we don't see him put one on, and there's no indication from the last time we saw his face that his scar started to bleed. (00:47:00)
Factual error: In his final speech to Willard, Colonel Kurtz talks of the Vietcong's "genius" for chopping off the arms of children inoculated against polio. While polio was technically available in both an oral form and an injectable form, any soldier administering the vaccine in SE Asia during the time would most certainly be administering the oral vaccine, and not giving a shot in the arm.
Continuity mistake: As they stop at the Playboy Bunnies' camp, two barefoot soldiers run out to meet them. When they first come out there's a red and white oil drum standing in front of their tent. In the next shot it's overturned but later when they walk back into the tent it's upright again. (01:22:55)
Continuity mistake: As they leave Colonel Kilgore on the beach at Vin Drin Dop the boat sails off to the left of the screen towards the bridge that was destroyed earlier in the attack. If you look at the far left of the screen there's a small Vietnamese temple with no fire anywhere near it. As they pass closer to the temple a large fire is now burning in front of it. (00:51:50)