Revealing mistake: When the cable car is seen in long shot coming down from the hill (carrying the film's heroes) it is painfully obvious that while the cable car is real enough, the mountain behind it is fake.
Continuity mistake: When Smith fires at the last German Kübelwagen chasing his team on the Oberhausen airfield runway, the scene alternates between two perspectives of Smith firing from the bus's engine cover: One from the front, the other from his backside. In each of these alternating shots, Smith holds the front part of his MP40 in a different grip. (02:20:55)Daniel4646
Factual error: A number of the German uniforms in this film are incorrect for this period and location. The reversible white/camouflage parkas worn by the allies were scarcely seen beyond the eastern front before D-Day and would have looked very suspicious without the matching over-pants. Additionally, the marsh pattern camouflage on these didn't appear on these until mid 1944, which only partially replaced the Heer splinter patterns, SS camo patterns, as well as blue and olive solids. Finally, the stereotypical black SS uniforms seen in the film were largely replaced with an olive green version of similar cut nearly 10 years before the film was set. In 1943-44, it was only worn by Himmler (who also wore the olive version), his staff, very highly placed members of SS related organizations, some of Hitler's bodyguard detachment, and native security forces on the eastern front (hiwi's).
Continuity mistake: The camera is looking down on Smith as he climbs up the rope and there are no footprints in the snow on the roof of the cable car room below him. The camera then cuts away to different angles but when we see the same shot of Smith a few seconds later there are clear heavy foot prints in the snow on the roof. (01:09:40 - 01:10:10)
Continuity mistake: When Eastwood gets off the German motorbike after the escape from the town, the seat of his trousers are wet but 2 seconds later are bone dry.
Other mistake: When escaping down the walls by abseiling, the actors hold rope with two hands - impossible to do down such a height with small width of rope. The stunt folk have rope going round their backs as they come down, abseiling properly.