Plot hole: As the Spanish fleet looms out of the fog, Hornblower is able to identify individual ships, a remarkable feat since every ship is wearing the same paint job.
Plot hole: When Knut and Rolf are setting the bombs in the engine room of the Hydro ferry, they are interrupted by a German soldier who they quickly overpower and kill. Why don't the Germans then notice that this soldier is missing? The clocks attached to the bombs show the time around 01:35am when the soldier is killed yet the alarm still hasn't been raised when Rolf catches the ferry several hours later at 9am. This is far too long for any soldier to be on sentry duty without reporting in to the Guardroom. The Germans would have known that the soldier was on duty on the ferry and when he didn't report in then they would have searched the boat thoroughly and found the bombs. (01:51:30)
Plot hole: The movie is allegedly set about ten years after the death of the German soldiers, since the daughter of one soldier is in her early teens. But none of the items in the scenery look like they're out of the fifties.
Plot hole: David couldn't have seen Sutherland's photos because Sutherland hadn't had time to develop them yet. Even if he did, it would have been difficult to find a lab that wouldn't turn him in as a spy. Overall, it would have been much safer to have the film processed in Germany.