Complete lack of explanation of the overall picture
I know the history, but for those viewers unfamiliar with the era, they would be totally confused about the true, more active background to the Dunkirk event.
I overheard someone else in the cinema asking their partner why the army and RAF weren't fighting inland to stop the Germans reach the coast?
The British/French armies were, of course, fighting bitterly against even the Waffen SS units in a huge but shrinking perimeter to halt the inevitable tide.
But all we got at the beginning of this film was a brief inadequate note of a few sentences?