Plot hole: Why do all the Germans abandon the cable car control room after the alarm has been sounded? If the cable car is critical for access to the castle then you would expect a hard core of SS troops to remain behind to control access and protect the machinery in the event of an attack. (01:42:55)
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. (02:06:00)
Factual error: The Germans in the castle are using Bell 47 helicopters which a) were American, not German, and b) weren't even in operation until 1946.
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.
Factual error: The aircraft at the Oberhausen airfield at the end of the field are T-6 texan trainers of the Austrian air-force painted with Luftwaffe markings.
Revealing mistake: After the accident with the German car crashing into the pile of snow in which the Germans were killed, Schaffer first hangs an MP40 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. (00:50:10)
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.
Factual error: In the flashback scene where the commandos are being briefed on their mission, they are told that General Carmody was on his way to a meeting with Russian officers on Crete. Hardly the best place for a meeting between the Allies since Crete was then under German occupation.
Continuity mistake: When Smith is driving the bus, there are at one point several bullet holes in the bus' windscreen and in the next shot they have vanished.
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.
Plot hole: A minor point but no mention is ever made of the pilot who deliberately crash-landed General Carnaby's plane at Oberhausen airfield. Presumably he would also have been taken to the castle for questioning but I suppose this would have further complicated the plot and be another person needing to escape.
Continuity mistake: Smith puts on one glove just before he hops onto the cable car with the two German spies. The next shot shows him with two gloves on.
Plot hole: The radio set used to communicate with headquarters in England was in fact a British low power VHF transceiver with a range of a couple of miles at best. It simply didn't have the capability to reach England.
Plot hole: How could Colonel Turner both be in London during the mission and in the pick-up plane? A Juncker can fly approx 220 km/h. It is approx. 1200 km from London to Southern Bavaria. That means that Colonel Turner would have had to leave London 5½ hours before the pick-up. The team does definitely not spend 5½ hours from the last time we see Colonel Turner in London until the pick-up.
Revealing mistake: As the spy troupe prepares to leave by airplane, a Kübelwagen with soldiers comes up, which Burton shoots with his MP40. As the car bursts into flames, the driver and passengers are revealed as dummies, since no one could or would sit around quietly while they were on fire.