Corrected entry: Evidently the Upkeep's design was still secret. In all the shots of the Wellington test drops some one has taken the trouble to go over the bomb with some kind of marker pen making it appear as a large black blob. You never see footage of the real Lancaster test drops. The Mosquito seen later is not dropping the upkeep but a smaller anti shipping version that didn't work, and hence was shown uncensored. A Mosquito couldn't possibly have lifted a full size upkeep mine.
Corrected entry: A train is shown being wrecked by the floods, dramatically crashing off the right hand track as it approaches us. German trains run on the left hand track.
Correction: You don't see the track. Water is already flooding the railway and the train is derailed when it hits it. It looks like a single line anyway, but the swirling water makes it impossible to tell.
Corrected entry: In the movie, the Castle that is set above the Eder-Dam is on the lake's southern side, but it is actually on the lake's northern side.
Correction: Copied off IMdB.
Corrected entry: The spotlight method of altitude finding depended on the plane being level. But during the first practice flight at 60 feet, we hear the crew member's altitude instructions go right on without a break while we are also seeing the plane bank steeply for a sharp turn.
Correction: This really happened. The Lancaster involved - M for Mother - nearly ditched in Eyebrook Reservoir in Lincolnshire as a result.
Corrected entry: The Bouncing Bomb was still on the secrets list when the film was made in the fifties. The makers of the film made the mock up bomb too big. It would have intruded right into the Lancaster's fuselage, through the main spar, and the wings would have fallen off.
Correction: The filmmakers were granted unprecedented access to footage of the real Dam Busters in action, including test flights and dropping of the 'Upkeep' bomb. The Lancasters you see flying were the real thing - and the 'mock up bombs' fit perfectly underneath and forward of the main spar, just like the real, smaller bombs did.
Corrected entry: Gibson's black Labrador dog ("Ni**er" - not then politically incorrect!) was accidentally killed the day before the mission, not on the day of mission, and was not an unknown hit-and-run. Presumably changed for dramatic effect.
Correction: This is a self correcting entry. This film is a partially fictional account of the events leading up to the famous raid, and it contains many historical inaccuracies. It is not a documentary and does not claim to be.
Correct, in the US release the dogs name become "Trigger".
Correction: This is hardly a fair criticism of a film made in 1954, and it doesn't really constitute a film mistake. They had to put a story based on a genuine historical event on the screen when the facts about that event were still protected by the Official Secrets Act, and by and large they did a good job. The Dam Busters is acknowledged as a partially fictional version of the famous raid, made in a time when special effects were primitive (on modern standards), and in their version of events the test drops of the Upkeep bombs were made by Mosquitoes, only two dams were attacked (five, in reality) and Guy Gibson thought up that method of setting the altitude of the bombers by watching the spotlights at a strip show. All fiction, of course, but in this film's reality, it is fact - and that's all part of the charm of this classic film.