Gordon Jackson shot scenes playing a RAF pilot but these were removed from the film
George Peppard was under contract with MGM and was desperate to be released from it. MGM agreed provided that he make one more film for them which turned out to be Operation Crossbow.
Richard Attenborough was offered a key role in this film
Around half of Richard Johnson's scenes were cut.
Average Shot Length = ~6.7 seconds. Median Shot Length = ~6.3 seconds.
Despite receiving top billing, Sophia Loren only appears in a extended cameo role. Producer Carlo Ponti, Loren's husband, believed his wife's popularity in the United States would boost the film's chances at the box office and had her billed accordingly.
Duncan Sandys, a character in this movie played by Richard Johnson, was a real-life person. Sandys was Chairman of the British War Cabinet Committee for the Defence against German rockets and flying bombs. He was the son-in-law of British wartime prime minister, Winston Churchill and was wounded during the Second World War in Norway in 1941 which resulted in him having a permanent limp.
Film debut of Philip Madoc.
For the scene in which a street is wiped out by a V-2, the filmmakers actually destroyed a row of flats which were slated for demolition. The shot was, necessarily, done in one take.
For the section of the film where RAF Bomber Command raid the Peenemunde rocket research site the producers used the Avro Lancaster PA474 used by the Cranfield institute of technology. PA474 was painted in 83 squadron colours in the summer of 1964 for the movie. PA474 now flies as part of the RAF Battle of Britain memorial flight.
In this movie, the character of Hannah Reitsch, played by Barbara Rütting(as Barbara Rueting), was a real-life person. Reitsch was a German aviatrix and at one time Adolf Hitler's own personal pilot. During the Battle of Berlin, Reitsch attempted to persuade Hitler to escape from the city in a small lightweight Fieseler Storch airplane.
MGM executives did not know the German characters would be speaking German (with subtitles) until they saw the rough cut; they wanted to have the German dialogue dubbed into English, but director Michael Anderson persuaded them to keep the subtitled dialogue.
The character of Constance Babington Smith in this movie, played by Sylvia Syms, was a real-life person. She was a British military officer who in 1957 after the Second World War wrote the book, 'Air Spy: the Story of Photo Intelligence in World War II'.
The screen writing credit for Richard Imrie is a pseudonym for Emeric Pressburger.
The title was (briefly) changed by MGM for the US release to "The Great Spy Mission" because the studio thought that having the word "operation" in the title might make people think it was either a medical film or a Robin Hood-type movie, a genre that wasn't doing well at the box office at the time.
This film's title is the same code-name for the real World War II spy mission, which was code-named "Crossbow". After the Second World War, because of this movie's title, reference to these events popularized them as being "Operation Crossbow".