Factual error: The Germans in the castle are using Bell 47 helicopters which, apart from being manufactured by the enemy, did not even appear until after the war.
Factual error: The aircraft at the Luftwaffe airfield at the end of the field look like US Harvard trainers.
Continuity mistake: Major Smith forces Carnaby to reveal his true identity by firing a single bullet which fragments the upper section of his chair. Soon after when Smith stands behind Carnaby (revealed as Cartwright Jones) the chair is undamaged.
Continuity mistake: When the team are about to jump from the cable car into the river, the view from ground level shows a bare road with no snow on it on the right and a line of trees on the left with German trucks parked next to them, but the view from the cable car shows a snow-covered road and no trucks beside the trees.
Revealing mistake: After the accident with the German car crashing into the pile of snow in which the Germans were killed, Schaffer first hangs a rifle on his shoulder and then somehow pulls up a body with only one hand. And with the changing of the grip, (from chest to legs) the 'body' stands on his own feet to give Schaffer the time and opportunity to do it properly.
Other mistake: In the scene where Burton and Eastwood are in the radio room, two grenades are thrown, which blow the main radio room door off the hinges and Burton and Eastwood run behind the small door and hide in that room. The German soldiers then run up and one of them throws another grenade supposedly into the radio room. However, the actor in his attempt to throw the grenade into the room instead throws the grenade into the door and it bounces back into the hallway in which he is standing and lands in front of him, yet no one reacts to this and seconds later we see an explosion as if the grenade had actually gone into the room, but it is really on the floor in front of the door and would have certainly blown the German soldiers to bits.
Continuity mistake: When Smith and Schaffer intrude on Carnaby's interrogation, the Gestapo officer and Mary are having drinks in the café, where he makes a statement that might reveal a fault in her identity (a location in Dusseldorf). Her hand is fixed on her chin, but the next cut shows her hand fully on her cheek.
Continuity mistake: After looking at the Castle, Smith sends Shaffer back to the others to tell them to stay behind the tree line and he goes to the radio to contact London. When he turns to go to the radio his MP40 has the butt extended, but when he gets to the radio it's folded back again.
Character mistake: In the courtyard of the castle there is an anti-aircraft gun. You could probably not find a worse place for a gun like that even if you tried (except maybe if you put it inside, in a windowless room). In the position it is placed it can only fire at targets directly ABOVE the castle. What you want to do is fire at targets BEFORE they reach the castle. It would be better if they placed it on the roof, or even near the village below.
Continuity mistake: When Burton and Eastwood jump from the cable car into the river, Burton jumps before Eastwood. However, the next shot downward has the Eastwood stuntman landing in the river first with the Burton stuntman still above him. We know it's Burton because of the bandaged hand.
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.