Esmond Knight, who had lost an eye during the war, had not yet regained the use of his remaining eye when he played the role of von Schiffer. Playing his part completely blind, there is only one scene when the audience can guess Knight's disability. It occurs quite briefly when Knight, about to go through a doorway, is gently steered through the door by a fellow actor.
Emeric Pressburger wrote the original story, but was unhappy with the way it was handled, especially the way the brutality of the Nazis was diminished, so he didn't allow his name to be used as a writer. He was happy to leave his name on this movie as a producer.
The Cammel Laird shipyard in Merseyside doubled for the Dutch shipyard. In the scene where Jaap van Leyden, played by Sir Ralph Richardson, defuses the bomb, Liverpool Anglican Cathedral can be seen clearly in the background.
This opening prologue is a quotation from writer John Webster (1580?-1634) from his play The Duchess of Malfi, Act IV, Scene 2. It states: "I know death hath ten thousand several doors. For men to take their exits."
Pieter Pietersen Heyn (1577-1629), known as Piet Hein, was a Dutch Naval officer and folk hero during the war between the United Provinces and Spain. In 1628, Hein captured a Spanish treasure fleet, the "Silver Fleet", loaded with silver from Spain's American colonies and the Philippines. Sixteen Spanish ships were intercepted and Hein captured over eleven million guilders of booty (comprising gold, silver and other trade goods) without any bloodshed.