Trivia: Len Deighton, the author of the original novel, also published a series of cookery books and wrote and drew a weekly strip cartoon-style illustrated cooking guide in London's The Observer newspaper - titled 'Len Deighton's Cookstrip'. In the first kitchen scene, where Harry Palmer is making coffee, you can see one of these strips is pinned to the wooden post next to the table.
Trivia: The ship used for the exterior close-up scenes was the Royal Navy frigate HMS Wizard. Some of the crew were used as extras in the film.
Trivia: The 'whistling' heard in the background before the opening credits is that of the director Sergio Leone.
Trivia: The voice of the mysterious host U.N. Owen is an uncredited Christopher Lee. (00:15:20)