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: 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.
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.
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.
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.