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".
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!
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.
This movie was never released in Brazil, due to the "coup-d'etat" organized by the military (1 April 1964). The generals who overthrew the government saw the film as uncomfortably close to what they did in real life and did not want Brazilians to be reminded of it, so they banned the film.
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.
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.
Paul Girard (Martin Balsam) meets Adm. Barnswell (John Houseman), commander of the 6th Fleet, in Gibraltar aboard his flagship, the USS Kitty Hawk, one of the newest and 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 second-longest serving U.S. Navy ship after the U.S.S. Constitution, "Old Ironsides," (commissioned 1797, and still on the Navy's list of active warships).
According to director John Frankenheimer, the Gen. Scott character is an amalgam of Gen. Curtis LeMay and Gen. Douglas MacArthur. The novel's co-author, Fletcher Knebel, has said that he based the character on disgraced and cashiered former army general Edwin Walker, who was forced out of the army after having been found to be using political material from various ultra-right-wing organizations he belonged to as "training manuals" in order to indoctrinate his troops in far-right-wing politics.
According to Kirk Douglas a scene that was shot but not used had Burt Lancaster's General Scott die in a car accident. It was ambiguous whether it was an accident or suicide. In its final cut his last scene in the Judas confrontation with Douglas.
In the original novel upon which the film was based, Adm. Farley C. Barnswell's flagship is the USS Eisenhower, a good guess on the part of the novel's writers, 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.
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 Gen. 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 (1955).
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, as well as a conversation in which the next Presidential election is "a year and nine months" hence, the most likely setting for these events is May 1975.
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 film is set in the near future (relative to 1964), but the exact date is never given. While subtle clues in the film suggest that it is most likely set in May 1975, Senator Prentice's limousine has registration stickers on its license plate for 1969 and 1970.