John Larkin, who plays Colonel Broderick, died suddenly less than a year after the film was released. Larkin had already shot many other films and TV episodes, which were released or aired posthumously.
Kirk Douglas had originally signed to play Gen. James Mattoon Scott. Douglas eventually realized that his friend Burt Lancaster would be ideal as Scott, and took the less flashy role of Col. Martin "Jiggs" Casey after Lancaster signed on to the film.
John Frankenheimer had been in the Air Force and was very familiar with the Pentagon.
According to director John Frankenheimer, the Gen. Scott character is an amalgam of Gen. Curtis LeMay and Gen. Douglas MacArthur.
An important plot point in the film involves the attempted coup taking place on the same day as the Preakness Stakes horse race. However, the seven-day timeline for the film would have had the coup taking place on Sunday while the Preakness is always run on a Saturday. John Frankenheimer said that the problem was solved by a scriptwriting acquaintance of his. This man worked as a script doctor and liked to gamble but wagered his professional services instead of money. Frankenheimer had won some work from the man and gave him the problem. The solution? In one scene a character walks by a poster which says "First Ever Sunday Running of the Preakness".
Both the book and the movie suggest that the story takes place in the near future -- that is, after the early 1960s. Using the day-date combinations featured on screen, the most likely setting for these events is May 1969.
Col. Casey's first name, Martin, is never spoken; he is always addressed (or referred to) by his nickname, "Jiggs". Casey's full name can be seen on the window that separates his office from the waiting room outside General Scott's office.
During a briefing between Col. "Jiggs" Casey and Gen. Scott in Scott's Pentagon office, the second shot on the video screen, allegedly of B-47s taxiing at Wright Field during the January alert, is footage from the film Strategic Air Command.
For security reasons, the Pentagon forbids camera crews near the entrances to the complex. John Frankenheimer wanted a shot of Kirk Douglas entering the building. So they rigged up a station wagon with a camera to film Douglas, in a full Marine colonel's uniform, walking up the steps of the Pentagon. The salutes Douglas received in that scene were real, as the guards had no reason to believe it was for a movie!
In the original novel upon which the film was based, Admiral Farley C. Barnswell's flagship is the USS Eisenhower, a good guess on the part of the novelists Fletcher Knebel and Charles W. Bailey II: an aircraft carrier of that name would not be ordered until 29 June 1970, a full eight years after the book's publication.
Originally scheduled for release in December 1963 but Burt Lancaster insisted the release date be postponed as it was too soon after the assassination of President John F. Kennedy. The same fate befell Dr. Strangelove or: How I Learned to Stop Worrying and Love the Bomb, which was also scheduled for a December 1963 opening.
Paul Girard (Martin Balsam) meets Admiral Barnswell (John Houseman), commander of the 6th Fleet, in Gibraltar aboard his flagship, USS Kitty Hawk, one of the newest & largest aircraft carriers in 1964. The scene was filmed in San Diego Bay, where the Kitty Hawk was actually flagship of the 7th Fleet based in the Pacific. The aircraft carrier USS Midway is in the background. The Midway is now a museum in San Diego while the Kitty Hawk was decommissioned (2009) and in the naval reserves. At time of her decommissioning, the Kitty Hawk was the longest serving US Navy ship.
Some film reference works (e.g., the multivolume set, "The Motion Picture Guide") incorrectly list Jack Mullaney's character as "Lt. Hough". "Hough" is the last name of this character in the novel upon which the film is based.
The "Eleanor Holbrook" subplot was based on a real-life incident involving Gen. Douglas MacArthur. In 1934, the general sued journalists Drew Pearson and Robert Allen for libel. He dropped the suit when the defendants announced they intended to take testimony from Isabel Rosario Cooper, a Eurasian woman who had been the general's mistress.
The White House wanted the film made and was very cooperative with the production. Press Secretary Pierre Salinger arranged for the production designer to have access to President John F. Kennedy's office and other rooms so they could be duplicated exactly at the studio.
This movie was never released in Brazil, due to the "coup-d'etat" organized by the military (1 April 1964). The plot and real life were too close.