Factual error: One of the shots of individual British Lancaster bombers approaching one of the dams is actually and incorrectly an American B17, seen for only a second or two. [At no time in the film is a B17 visible in the British release of the film. However the B17 crashing appears in a version of the film released in the U.S.A.]
Trivia: A (corrected) entry states that a USAAF B-17 'Flying Fortress' bomber is visible in the film. In fact in some prints produced for release in the US irrelevant stock footage of a B17 was randomly cut into the film to make it more acceptable to American audiences. This was a deliberate alteration of the film done very much against the wishes of the producer and director, and it explains the 'error' - the contributor has seen one of the non-canon US prints.