New this month Factual error: When the returned soldiers are on the train at the end of the film, it's an open plan post-war British Rail Mark I type, which where built from around 1950. Also the blue upholstery on the seats looks to be the corporate blue introduced by British Rail in the 1960s, used by the preserved railway owning the stock, and not what would have featured in Southern Railway carriages of the time. The carriages also have horizontally-sliding windows, which are far more contemporary than wartime trains, which had windows with a much larger vertical opening, held in place by a leather strap.
New this month Factual error: In the silent overfly of the plane that ran out of fuel in the background you see a lot of modern architecture that is definitely not from the 1940s.
New this month Factual error: Near the start of the film in the harbour when the camera pans around to the left looking out to sea, you can see the back of the modern Weymouth Lifeboat 17-32 moored up in the background.
New this month Factual error: When the boat returns to England they state the cliffs are Dorset. There were 3 evacuation routes from Dunkirk - all to Kent. It would be nonsense to sail from Dunkirk to Dorset as you have to almost pass Dover on the way! (never mind the fact the boat would probably not have made it without refuelling).
New this month Factual error: Not until the very end of the 10-day evacuation were the French (or British for that matter) defending the very beaches themselves, and yet the movie opens with the French roadblock doing just that.
New this month Other mistake: In a scene where the commanding marine officer stands on the mole in a close-up shot, black smoke is rising from sky out of nowhere. Looks like the FX guys forgot to delete the particle effect after deciding to not show a boat with its exhausts in the background.
New this month Character mistake: The story arc set on the Mole covers one week. The Highlanders attempt to refloat the beached trawler on the last day of that week. One of them confidently states that the tides are three-hourly. (The audience know this isn't true because we've seen a similar conversation between the Admiral and the Colonel.) At least some - if not all - of those Tommies have been on the beach all week. Have none of them have noticed that the tides are six-hourly?
New this month Factual error: Oriented strand board (OSB), also known as sterling board, sterling OSB, aspenite, and smartply in British English, was not invented until 1963. The French warehouse floor was covered with it. See blood spot close up.
New this month Factual error: One of the dams in or around Dunkirk has a foundation made of tetrapods. These concrete structures were developed in the 50s, according to wikipedia (https://en.wikipedia.org/wiki/Tetrapod_ (structure)).
New this month Factual error: 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.
New this month Deliberate mistake: The me-109 have painted yellow fronts, this wasn't done by the Germans until after Dunkirk. Christopher Nolan has admitted doing this deliberately so the audience could tell the difference between the spitfire and the me-109 during the combat scenes.
New this month Continuity mistake: As the lone Spitfire trails and attacks the German bomber, we see smoke trailing from the right bomber engine. In the next scene, no smoke; the next scene the Spitfire continues the attack, and the smoke starts anew.
New this month Factual error: Generally the clothes are not 100% of WWII. We see a lot of hats and head protection which didn't exist at that time. Also the holsters for the side guns were all closed and not open like in the movie.
New this month Continuity mistake: In the scene at the end of the film featuring a Spitfire that has ran out of fuel, we see the plane with the propeller stopped but in the next shot, it's slowly rotating. The next shot shows it stopped again but in the next shot, it's (once again) slowly rotating.
New this month Factual error: As the last Spitfire runs out of fuel, it continues to fly along the beach; then apparently turns around and flies the opposite direction along the beach still maintaining his steady low altitude. This is an impossible feat as distance flown (and any turn without power) results in loss of altitude.
New this month Factual error: When asked whether he had a gun, Cillian Murphy says he had a .303. As an officer, he would have carried a pistol but not a rifle. It was not until later in the war that British officers began to carry weapons other than sidearms, and even then it was usually SMGs and not rifles.
New this month Deliberate mistake: Christopher Nolan admits he used a French destroyer instead of a British destroyer, for practical purposes (most people won't notice).
New this month Factual error: Colonel Winnant wears a regimental cap badge. In fact, full colonels (as he is) and brigadiers have a different cap badge (a lion standing on a crown). It's not entirely beyond the realms of possibility that he would choose to continue to wear his old cap badge, but it would be very unusual (and completely against regulations).