Deliberate "mistake": In the approach to Dunkirk, Robbie is carrying a pistol, complete with webbing holster. He has no rifle and is carrying a bayonet on his haversack, presumably not having the usual belt frog to carry it more easily. As a Private (this is emphasized in the dialogue) in an infantry regiment, he'd have carried a rifle and not a pistol. Although he might have acquired the pistol during the retreat, he's less likely to have changed his webbing order to match. This may be a deliberate directorial choice. The dialogue emphasizes his natural "officer qualities", and that his prison record has prevented him from becoming one. The wearing of officer's equipment, even if historically inappropriate, also reinforces this and distinguishes him from his comrades.

Continuity: When Briony sees Cecilia coming out of the fountain (from Briony's perspective), Cecilia steps out of the water with her right foot first. When we see the same scene afterwards, from Cecilia an Robbie's perspective, Cecilia steps with her left foot first.

Factual error: On arriving on the beach at Dunkirk, Robbie is told of the sinking of the Lancastria and the loss of 3000 men. This event actually occurred 17 days later on June 17 1940.

Continuity: In the love making scene in the library, Robbie pulls down the strap of Cecilia's dress and she pulls her arm out. In the next shot it is up and over her shoulder again.

Continuity: When Briony walks in on Robbie and Celia in the library, the door is slightly ajar (since it's the lamp in the room that catches her attention). But when the scene is replayed from Robbie and Celia's perspective, Robbie shuts the door completely.

Continuity: In the scene by the fountain from Briony's point of view, when Cecilia takes her top off she pulls the strap of her undergarment twice. However, from Robbie's point of view, she doesn't pull the straps at all.

Factual error: The early scenes in Atonement take place, according to the opening caption, in "England 1935" on a single summer's day. The action shifts at the beginning of scene 9 to "Northern France four years later" according to the caption. This, then would have been the summer of 1939 when Britain wasn't yet at war. The Dunkirk retreat took place in the summer of 1940, five years after the action in scenes 1-8.

Factual error: In the section of the movie set in 1935, there is a scene where Robbie is daydreaming and the image of a four engined bomber crosses the screen. The image is of a Short's Stirling (the tail configuration is markedly different to the Lancaster), an aircraft which did not enter service until 1939.

Continuity: When Cecilia and Robbie are having sex against the bookcase, a close-up reveals she slips her left foot out of her shoe. But when Briony walks into the room and the two lovers are shown motionless, we see Cecilia still has both shoes on.