Factual error: The final scene of the movie has Col. Kirby and the little Vietnamese boy supposedly on the beach at Da Nang, Vietnam. Kirby is saying, "The future of 'nam is you, kid", and the camera pans out to the sea and the sun is going down. The sun's sinking in the east...
Suggested correction: Nowhere in the film are we told where in Vietnam the Green Beret base is, just that it is in South Vietnam (of course). South Vietnam has a Western coast, along the Gulf of Thailand, along which anyone can watch the sun set over the sea.
Around the 18:00 - 18:30 mark a character welcomes John Wayne to Da Nang. This base is returned to throughout the film, including the infamous sun setting in the east scene. Da Nang's beaches face to the Northeast. Only when you get south of Nha Trang does the Vietnamese coast begin to offer a south to southwest horizon on the ocean.
Plot hole: Why do all the Germans abandon the cable car control room after the alarm has been sounded? If the cable car is critical for access to the castle then you would expect a hard core of SS troops to remain behind to control access and protect the machinery in the event of an attack. (01:42:55)
Factual error: The German tanks are American M47s, post WW2. They had the same hulls as the M46s (also post-WW2), but a better slope and greater effective armor on the turrets.
Revealing mistake: When Buck and the gang ride away from the saloon in Dallas where JC made a few new 'friends', the footage is sped-up for a second just as soon as James Caan jumps on his horse. (00:05:50)
Continuity mistake: When Gregor and Willie are attacked by the German convoy, they pick up two discarded StG 44s, but in th next scene they are firing AK-47s which had not yet been invented. After the battle, they are again carrying StG 44s.