Continuity mistake: At the briefing before Halloran's second mission there are three bright ceiling lamps switched on in the hall. Immediately after the briefing Col. Bart wants to have a private word with him and the lamps are switched off, without any visible change of lighting. (00:28:25)
Continuity mistake: The informant who calls the Germans when Halloran and Sellinger hide in the barn is wearing only a shirt when he is seen behind the curtain. A moment later, when he makes his call, he is wearing a jacket and a hat. Why would he put those on just to make a phonecall? (01:30:00)
Factual error: Lots of mistakes regarding spy craft and military intelligence protocol. Sellinger would not be carrying a locket with a picture of Margaret when he is dropped into France as an SS officer. Halloran would not know the name of the spy (Wells) they were waiting for to drop into France. Wives (Margaret) would not be allowed in to offices of Intelligence HQ.