Trivia: The idea of helicopters was not necessarily new in WW2, but effective designs were not made until after the war; there is evidence from some literary sources (one of them being a book named "German Secret Weapons of WW2" or something like that) that the Germans did indeed conduct experiments and designs on this vehicle type.
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.
Chosen answer: This is not unusual in older films. Earlier costume designers were less attentive to historical accuracy and freely incorporated current fashion trends into period movies. It was just an accepted practice and movie audiences back then were often less discerning and/or unaware of inaccuracies. Today's costumers have greater access to historical information, do more research, and strive for authenticity.
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