- Backed by the Pentagon: The Air Force supplied the production with assistance and equipment, including a dozen used B-17 bombers gathered from the Air-Sea Rescue Service and retrofitted to their combat configurations. The airborne combat scenes were created with actual wartime footage taken by cameras on both American and German planes, which meant that only landings, takeoffs, and close-formation maneuvers had to be shot expressly for the film. That said, after reading the completed script, officers at the Pentagon were uncomfortable about Savage's breakdown under excessive strain, saying they would "prefer not to indicate to the public that a commanding general...became as irrational as indicated." Such a high-ranking officer might suffer from "physical ailments, nervousness, short temper or just plain fatigue, but he would never "burst out hysterically or have a complete mental collapse." The screenplay was modified to give Savage a quieter, more subtle breakdown. Other revisions made at the Air Force's request included toning down the heavy drinking and having the chaplain watch other men playing poker, not joining in the game himself.
- Doubling for London: Although ostensibly set in England, most of the film was actually shot in the USA. This would explain why the general is driven around in cars that are clearly left hand drive instead of right hand drive as they are in the UK.
- Executive Meddling: A romantic subplot, which features in the book, was dropped at the studio's insistence. They wanted the script to concentrate fully on the psychological effects of war and the theme of leadership.
- What Could Have Been:
- The film was originally going to be shot in colour. This was changed to incorporate the aerial combat footage.
- The lead role was originally offered to John Wayne, who turned it down. Clark Gable (who flew a half-dozen combat missions in a B-17note ) was also interested. James Cagney and Burt Lancaster were also considered. Gable instead starred in a similar movie, Command Decision.
- William A. Wellman was attached to direct at one point. William Wyler was also interested.
Trivia / Twelve O'Clock High