Blu-Ray edition opening screen: "While we acknowledge some of the language used in The Dam Busters reflects historical attitudes audiences may find offensive, for reasons of historical accuracy we have opted to present the film as it was originally screened."
This refers to the fact that the protagonist, Wing Commander Guy Penrose Gibson's, dog is named "N-Word." In addition, the dog's name is used during the raid on the dams as code indicating the dam(s) have successfully been breached.