Donald Pleasence had actually been a Royal Air Force pilot in World War II, who was shot down, became a prisoner of war and was tortured by the Germans. When he kindly offered advice to the film's director
John Sturges, he was politely asked to keep his "opinions" to himself. Later, when another star from the film informed John Sturges that Pleasence had actually been a RAF Officer in a World War II German POW Stalag camp, Sturges requested his technical advice and input on historical accuracy from that point forward.
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