Passage: The film premiered on 13 July 2017 at Odeon Leicester Square in London, and was released in the United Kingdom and the United States on 21 July in IMAX, 70 mm, and 35 mm film formats. It is the highest-grossing World War II film, making $526 million worldwide. Dunkirk received praise for its screenplay, direction, musical score, sound effects, and cinematography; some critics called it Nolan's best work, and one of the greatest war films.

Question: What day was the film released in IMAX in the US?
21 July