Director 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.
Only eight U.K. military ambulances from World War II remain, and this movie made use of them all.
The small English town of Redcar stood in for the French city of Dunkirk, and the Dunkirk set built there was the most expensive one in this movie, costing an estimated one million pounds sterling.
The green dress which Keira Knightley wore in this movie has been named "the best of all time" by InStyle Magazine, exceeding some classics as Audrey Hepburn's little black dress in Breakfast at Tiffany's (1961), Marilyn Monroe's white dress in The Seven Year Itch (1955) or Vivien Leigh's red dress from Gone with the Wind (1939).