Factual error: The daylight air-raid on the Norwegian Heavy Water plant in 1942 was done by Boeing B17G bombers, with the distinctive chin gun turrets. These planes did not come into service until 1944, when they were introduced to counter the head-on attacks by German fighters.
Other mistake: Troops being flown in are in a glider towed by a bomber. People on the ground hear airplane engine difficulties and then a plane crashes. There's no attention paid to the people in a glider. They assume all have perished, but where are the people in the glider?
Plot hole: When Knut and Rolf are setting the bombs in the engine room of the Hydro ferry, they are interrupted by a German soldier who they quickly overpower and kill. Why don't the Germans then notice that this soldier is missing? The clocks attached to the bombs show the time around 01:35am when the soldier is killed yet the alarm still hasn't been raised when Rolf catches the ferry several hours later at 9am. This is far too long for any soldier to be on sentry duty without reporting in to the Guardroom. The Germans would have known that the soldier was on duty on the ferry and when he didn't report in then they would have searched the boat thoroughly and found the bombs. (01:51:30)
Continuity mistake: In the scene when Richard Harris and Kirk Douglas parachute back into Norway, there is a white parachute blowing in the wind. Kirk Douglas goes to collect it, but there are footprints already in the snow where they have previously filmed a retake. (00:27:00)
Continuity mistake: At the beginning of the movie in the scene where the German convoy is driving down the mountainside the Colonel (Terboven) is sitting in the left seat of the Mercedes, after the scene where the Germans are stopped by the huge bolder, he gets out of the left side door, he shouts orders to Frick, the convoy then continues down the road, shortly after the credits roll in a continued scene the camera shows him sitting in the right side seat. (00:01:00 - 00:04:40)
Other mistake: When Knut and Rolf leave Anna in the car on their way to plant the explosives on the ferry, they instruct her to wait no more than 2 hours for them. Once on the ferry, the earliest time seen on the alarm clocks is about 01:10 so we can assume that Knut and Rolf left Anna sometime before 01:00. When they return to the car after the explosives have been planted, you get a brief glimpse of Anna's watch which shows the time as 03:35; a full 2 hours 25 minutes after the 01:10 we saw on the clock yet Anna states that there are 9 minutes left. (01:44:06 - 01:53:57)
