Continuity mistake: At the start the damage to the wooden gates changes between shots. (00:02:10)
Continuity mistake: There's a repeated issue with weather continuity throughout the movie. Many scenes cut between daylight, sunset and cloudy weather literally seconds apart. This has nothing to do with the particular time structure of the movie, since it happens between shots and reverse shots of the same scenes. These inconsistencies are particularly obvious at the opening scene, at the Stuka bombing and at the rescue of the shivering soldier. In these scenes, weather turns from heavily cloudy to fully sunny just from one shot to the next. (00:26:20)
Continuity mistake: When the Stukas are shown bombing the beach, they drop a single bomb, but from beach level, you see sticks of bombs landing.
Suggested correction: The Stukas are dropping SD-2 canister bombs, a particularly nasty anti-personnel weapon. Upon release from the aircraft the bomb divided into the bomblets you see here.
First known use was bombing of England, no evidence they were used at Dunkirk. Also, the SD-2 was smaller and produced numerous small explosions. The ones we see in Dunkirk are larger and much bigger than anything the little SD-2 could ever produce - so the original criticism sticks.
Continuity mistake: The sea often changes state from shot to shot. One minute we've got a reasonable Force 4 blowing and some surf, the next it's 'sea like a mirror' and then there's everything between.
Continuity mistake: As the lone Spitfire trails and attacks the German bomber, he hits the right engine, which starts smoking but the trail quickly fades. He then hits the left, which smokes a lot. We then see the same attack from below, and from this angle the both engines are smoking equally badly.
Continuity mistake: When the two British soldiers are exchanging a bottle of wine, it's full in one shot but when given to the other soldier it's suddenly less so.
Continuity mistake: During the spitfire scenes over the channel, it's day light, however, when one of the ships was bombed and the soldiers jump over board, it's pitch black. Several cuts between these scenes each time show daylight in one and night in the other.