Revealing mistake: In the final Indian chase at the conclusion of the film, when a covered wagon rolls over, one can see the rope that was used to ensure it tipped over.
Continuity mistake: When Sylvia and Dr. Forrester are in the farm house, Sylvia cooks some eggs, then places the plates of eggs on the table. As she places them down you can see a plate with toast stacked on it. This plate disappears in the next shot of them both sitting down. (00:42:40)
Revealing mistake: In the scene where Lancelot runs into and fights Arthur's ambushers, he runs one of them through with his sword. It is visible that he stabs his opponent past the body, but close enough for the appearance.
Factual error: If we are to assume that the British cruisers were Dido class with 5.25" guns, the assertion that the Essen would outrange them by 5000 yards is pretty much true. However, in order for the Brits to launch torpedoes, they would have had to close to inside of 20K yards, well within range of their main guns. Thus said, if the British cruisers were any of their 6 inch gun class, there would have been no advantage in range.
Visible crew/equipment: John Payne leaves a theater after getting into a fight after being tricked by actress friend Evelyn Keyes during an audition. As he walks out the backstage to the back entrance, the shadow of a crew member (possibly the camera operator) can be seen on the wall as Payne passes by. (00:31:00)