Shooting the five minute Dunkirk beach scene was arguably the toughest portion of shooting. The shooting schedule dictated that the scene must be completed in two days, because the crew has limited time with the 1,000 extras. However the location scouts report indicated the lighting quality at the beach was not good enough until the afternoon of the second day. This forced director Joe Wright to change his shooting strategy into shooting with one camera. The scene was rehearsed on the first day and on the morning of the second day. The scene required five takes and the third take was used in the film. On shooting, Steadicam operator Peter Robertson shot the scene by riding on a small tracking vehicle, walking off to a bandstand after rounding a boat, moved to a ramp, stepped onto a rickshaw, finally dismounting and moving past the pier into a bar.
Joe Wright had wanted Keira Knightley to play the role of Briony in her late teens, but Knightley immediately liked the character of Cecilia, and also wanted to get away from playing girls on the brink of womanhood and play a more mature character for once.
As Robbie is hauled off by the police and his mother frantically yells "liar" while running up the road, Briony peers from a staircase landing through a window decorated with figures in stained glass. The figure in the window Briony stares through is labeled Matilda. This is an allusion to a famous children's poem by Hilaire Belloc entitled "Matilda", whose first line runs, "Matilda told such dreadful lies, it made one gasp and stretch one's eyes". By the end of the poem, Matilda has burned to death, having called wolf one time too many.
On the DVD commentary, director Joe Wright notes that the designer of Keira Knightley's green evening dress costume deliberately kept the seam down the middle of the skirt open (where it would normally be sewn shut in a dress design) for what Wright calls "easy access" in the library scene.
Local government in Redcar gave permission for a bandstand to be erected and for a shipwreck to be placed on the beach for authenticity. A number of houses along the beach front were painted to suit the era. The cinema, which looked the part already, merely had an advertisement painted on the side of the building to complete the set dressing. Everything was undone after filming was complete and Redcar seafront now looks like a normal seaside town again.
Vanessa Redgrave noted that "Saoirse Ronan and Romola Garai and I did some improvisations on body language, among other things, for Briony. Joe - who is brilliant with actors - was able to pick and choose what he wanted focused on during the filming."
According to Sandra Lean, widow of legendary filmmaker Sir David Lean - Joe Wright was apparently so impressed by Sir David's epic work that he screened most of it before making Atonement, and then instructed cinematographer Seamus McGarvey to also watch Lean's oeuvre, with the hope of being able to match some of the director's power. Ultimately however, Lady Lean felt she 'just didn't like the movie. I thought it was terrible and badly directed. Everyone goes on about the long shot of the beach at Dunkirk, but I thought it was boring and laborious.' Obviously they were trying to get the feel of a David Lean epic but they failed. Without David, it's not so easy.'
Richard Eyre was originally attached to direct the project. However, as time passed he became busy with another film project and stage play. The producers and himself decided that, if they could find a director they all approved of, he would hand the project over. Joe Wright was found.