Revealing mistake: After Smith and Schaffer are captured and while they are being transported by car, Schaffer pushes one of the guards out of the car and a struggle begins which causes the car to crash. After the crash, the body of the guard that was pushed out of the car magically appears about 50 feet behind the accident (just before the crash there was no body). (00:49:25)
Continuity mistake: After Smith and Schaeffer are done rigging the trees and poles with explosives, Schaeffer gets off the motorcycle and you can see the seat of his pants is wet. As they are entering the shed, the seat of his pants is now dry.
Factual error: As the coach moves through the village near the end of the film, it drives past a tracked vehicle. The vehicle is a Hotchkiss LPz, a type of armoured personnel carrier not produced until the 1960s.
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: 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: 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.
Factual error: Smith has the books with names in his pocket when he goes into the water, jumping from the cable car. When he shows the books to Turner, they are in perfect shape. They should have been waterlogged or at least showed some sign of water damage.
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.
Continuity mistake: In the scene where the group parachutes in, the sky is cloudy and we can see snowfall, but watch carefully, as the men make their way to the equipment containers and then to find Sgt Harod we constantly see shots switching between cloudy and snowfall, then to no snowfall and sometimes sunlight, then back to cloudy and snowfall again. This switch back and forth is even more evident on the closeups of Richard Burton.
Visible crew/equipment: In the scene where the Germans are pursuing Richard Burton's escaping party as they make their way towards the aircraft waiting for them, you will see the first of two pursuing German Kubelwagons being hit with machine gun fire and flipping. When this happens, you will see a cable used to flip the vehicle on the bottom left side of the screen being quickly retracted as it becomes detached from the Kubelwagon's axle.
Continuity mistake: In the scene where they all jump from the sky tram into the water after escaping from the castle, we see the blonde woman (Mary) swim to shore. As she gets out, her hair is absolutely soaked and matted to her head. When the angle of the camera changes, we see her only this time, he hair is almost perfect and only slightly damp and is actually blowing in the soft breeze.
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. (02:06:15)
Other mistake: When Mary first meets Major Smith in the shed on the alpine pasture she complains that she ‘nearly froze to death in that damn plane' yet when she emerged from her hiding place on the aircraft she was only just putting her gloves on. If she was that cold then she would have had the gloves on already. (00:09:05)
Continuity mistake: When Mary Ure goes to secure the rope over the wooden beam to allow Smith and Schaffer to climb into the castle, she starts by hitting a narrow piece of wood which comes loose. The scene then momentarily cuts to the guys on the cable car. When it cuts back to Mary, the narrow piece of wood is back in place and she is knocking out the much wider piece next to it. (01:05:15)