Revealing mistake: In the final scene where Fonda and Holbrook are looking over the carrier at the crowds on the dock you can see that only the first rows of people are dressed in period clothes, the rest of the crowd are dressed as they would have been in 1976 when the film was made.
Plot hole: Radl and Steiner discuss the entire scheme to kidnap Churchill on the Alderney docks - in full view and hearing of a number of civilians (who shouldn't be there, pace another posting), including local fishermen. Though the Germans banned all fishing activities in the Channel islands including Alderney in 1941, they were well aware that there was a flow of information from the island to military authorities in the mainland. Why would they be so stupid as to discuss a top secret military mission in public? In reality, they wouldn't even discuss it in front of their own men.
Revealing mistake: When the toggle on the gun is pulled back that supposedly injures Captain S. Melly's fingers, it doesn't actually make contact with them.
Factual error: When a Rear Admiral and Captain are walking together, the Captain's epaulets are the wrong way round. A cardinal sin in the Navy. (01:30:00)