Continuity mistake: There is genuine wartime footage of Spitfires of the the right type for the period, but other scenes have later (maybe even postwar) versions flying about.
Continuity mistake: In this scene we see Jack Hawkins in his office talking to a soldier before Alec Guinness enters the office. In the background is a book shelf. On the top shelf there are four books to the left of the shelf which are standing side by side. Then there are several spaces then other books leaning against each other. After Alec Guinness has been briefed he leaves and we get another look at the book shelf. This time the top shelf has five books on the left and where the spaces were one book lies flat on it's side.
Continuity mistake: Near the end of the film much is made of Alec Guinness' self sacrifice in breaking radio silence to report the position of a German-Italian convoy. In due course he is shot down by German fighters, only the convoy had already sighted him and were shooting at him, so his breaking radio silence surely wasn't going to make his position any worse. Although his Spitfire may have been able to outrun any enemy fighter, the film's last seconds make it clear that he was "jumped" ie. attacked from above where the German fighters were able to trade height for speed and gain on the Spitfire, a tactic feared by all pilots in that conflict.