When the troop ship taking the platoon home is bombed and sunk in Dunkirk harbor, the scene of the ship sinking is taken from Der große Atlantik (1953), which depicts the sinking of H.M.S. "Compass Rose".
The term "U-S" means 'un-serviceable' and is a British military term
The command center used by Vice Admiral Ramsey (Nicholas Hannen) was the real bunker used during the operation. It's part of a large underground complex beneath Dover Castle. It's open to the public. The balcony in the cliffs is visible from the ferry terminal below.
Strand Quay, on the west side of the town of Rye, was used for the Dunkirk perimeter. In one shot, the top of St. Mary's Parish Church may be spotted, and in another, we get a glimpse of the famous Mermaid Street in the background.
Approximately twenty minutes were cut for the U.S. release.