Continuity mistake: When the soldiers are ambushed by the Germans, they jump off and Jack Kelly is wounded in the arm, showing a torn shirt and bloody arm. Later when Audie Murphy is wounded and in the hospital Jack Kelly visits him. The only bandage on him is on his hand, which wasn't injured before.
Factual error: When Jimmy Stewart is almost down to the runway during the bad weather, the aircraft exterior shots show the type of cloud tops found only at high altitude, not low to the ground.
Continuity mistake: In the scene where Trevor Howard and José Ferrer are sharing what appears to be some port (about 50 minutes into the movie), the port decanter has a drip stopper in the long shot which disappears in the close-up shot of Leslie Howard and then re-appears in the following longer shot.
Factual error: The system devised to get the height right was, in the film, said to have been thought of by the 617 Sqn crews following a visit to the theater. In reality it was devised by the 'boffins' at Farnborough.
Suggested correction: See many previously posted 'mistakes' of this type and the standard correction: this is not a documentary and never pretended to be. It is a war drama and many facts were changed to fit the action.
Those correction are often made in fallacy. Dramas based on historical accounts have liberty to change small or inconsequential things, like adding a person that may have never existed, or change a relationship for dramatic purposes. Despite not being a documentary, unless it's a fantasy film, changes in historical facts are mistakes (for example, a drama can't have the Eiffel Tower in London just because it's not a documentary).
Suggested correction: This was the version given in Brickhill's book. The real story wasn't published till many years after the film was made.
Other mistake: While all the business signs in downtown Osaka are properly in Japanese, the local newspaper, The Osaka Times, is printed entirely in English.