Factual error: The Germans in the castle are using Bell 47 helicopters which a) were American, not German, and b) weren't even in operation until 1946.
Where Eagles Dare (1968)
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Directed by: Brian G. Hutton
Starring: Clint Eastwood, Richard Burton, Patrick Wymark, Mary Ure
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More mistakes in Where Eagles Dare
Mary Ellison: I nearly froze to death in that damn plane. Why couldn't you have supplied some hot water bottles or an electrically heated suit? I thought you loved me.
Major John Smith: Can't help what you think.
Trivia: When Mary goes undercover in the castle, her name is Maria Schenck. They are the middle names of Col Stauffenberg, the German officer played by Tom Cruise in Valkyrie, who tried to kill Hitler.
Question: When Richard Burton is holding his gun on all the people in the meeting and asks if one of the guards could come in and watch them, why doesn't the guard just shoot him?
Answer: When the guard comes in, Burton explains what's going on. Also he is dressed as a German officer so his explanation and actions are plausible.