Production notes

According to their files, 20th Century Fox paid $100,000 outright for the rights to the unfinished book, plus up to $100,000 more in escalator and book-club clauses. Darryl Zanuck was apparently convinced to pay this high price when he heard that William Wyler was interested in purchasing it for Paramount. Even then, Zanuck only went through with the deal in October 1947 when he was certain that the United States Air Force would support the production. The film made use of actual combat footage during the battle scenes, including some shot by the Luftwaffe. A good deal of the production was filmed on Eglin Air Force Base and its associated auxiliary fields near Fort Walton, Florida.

Screenwriters Bartlett and Lay drew on their own wartime experiences with Eighth Air Force bomber units. At the Eighth Air Force headquarters, Bartlett had worked closely with Colonel Armstrong, who was the primary model for the character General Savage. The film's 918th Bomber Group was modeled primarily on the 306th because that group remained a significant part of the Eighth Air Force throughout the war in Europe.

Clark Gable was interested in the lead role of General Frank Savage. Gable, who had served in the USAAF during World War II, played a similar role in the 1948 film Command Decision. John Wayne was offered the leading role, as well, but turned it down. Burt Lancaster, James Cagney, Dana Andrews, Van Heflin, Edmond O'Brien, Ralph Bellamy, Robert Preston, Robert Young, and Robert Montgomery were also considered for the role. Eventually, the role went to Gregory Peck, who initially turned it down because the script was similar to Command Decision. Peck changed his mind because he was impressed with director Henry King, finding his empathy with the material and the cast and crew appealing. The two made more films together: The Gunfighter (1950), David and Bathsheba (1952), The Bravados (1958), and Beloved Infidel (1959).

Veterans of the heavy bomber campaign frequently cite Twelve O'Clock High as the only Hollywood film that accurately captured their combat experiences. Along with the 1948 film Command Decision, it marked a turning away from the optimistic, morale-boosting style of wartime films and toward a grittier realism that deals more directly with the human costs of war. Both films deal with the realities of daylight precision bombing without fighter escort, the basic USAAF doctrine at the start of World War II (prior to the arrival of long-range Allied fighter aircraft such as the P-51 Mustang). As producers, writers Lay and Bartlett reused major plot elements of Twelve O'Clock High in later films featuring the U.S. Air Force, the 1950s-era Toward the Unknown and the early 1960s Cold War-era A Gathering of Eagles. Paul Mantz, Hollywood's leading stunt pilot, was paid the then-unprecedented sum of $4,500 in 1948 ($58,000 in 2024) to crash-land a B-17 bomber for one early scene in the film. Frank Tallman, Mantz' partner in Tallmantz Aviation, wrote in his autobiography that while many B-17s had been landed by one pilot, as far as he knew, this flight was the first time that a B-17 ever took off with only one pilot and no other crew; nobody was sure that it could be done. " The footage was used again in the 1962 film The War Lover. Locations for creating the bomber airfield at the fictional RAF Archbury were scouted by director Henry King, flying his own Beech Bonanza some 16,000 miles in February and March 1949. King visited Eglin AFB on March 8, 1949, and found an ideal location for principal photography several miles north of the main base at its Eglin AFB Auxiliary Field No. 3, better known as Duke Field, where the mock installation with 15 buildings (including a World War II control tower) were constructed to simulate RAF Archbury. The film's technical advisor, Colonel John de Russy, was stationed at Maxwell Air Force Base, Alabama, at the time, and suggested Ozark Army Air Field near Daleville, Alabama (now known as Cairns Army Airfield, adjacent to Fort Rucker). King chose Cairns as the location for filming B-17 takeoffs and landings, including the B-17 belly landing sequence, since the light-colored runways at Eglin did not match wartime runways in England, which had been black to make them less visible to enemy aircraft. When the crew arrived at Cairns, it was also considered as "ideal for shots of Harvey Stovall reminiscing about his World War II service", since the field was somewhat overgrown. The opening and closing scenes of the derelict RAF Archbury, referencing themes in the film, have a very similar approach to the opening scenes of the derelict fictional RAF Halfpenny Field in the earlier 1945 film The Way to the Stars. Additional background photography was shot at RAF Barford St John, a satellite station of RAF Croughton in Oxfordshire, England. Officially, the airfield is still under Ministry of Defence ownership following its closure in the late 1990s as a communications station linked to the since-closed RAF Upper Heyford. Other locations around Eglin AFB and Fort Walton also served as secondary locations for filming. The crew used 12 B-17s for filming, which were pulled from QB-17 drones used at Eglin and other B-17s from depot locations in Alabama and New Mexico. Since some of the aircraft had been used in the 1946 Bikini atomic experiments and absorbed high levels of radioactivity, they could only be used for shooting for limited periods. Twelve O'Clock High was in production from late April to early July 1949. Although originally planned to be shot in Technicolor, it was instead shot in black and white, allowing the inclusion of actual combat footage by Allied and Luftwaffe cameras.

Twelve O'Clock High premiered in Los Angeles on December 21, 1949, and opened in New York City on January 26, 1950. It went into general release in February 1950. An influential review by Bosley Crowther of The New York Times was indicative of many contemporary reviews. He noted that the film focused more on the human element than the aircraft or machinery of war. The Times picked Twelve O'Clock High as one of the 10 Best Films of 1949 and, in later years, it rated the film as one of the "Best 1000" of all time. After attending the premiere, the commander of the Strategic Air Command, General Curtis LeMay, told the authors that he "couldn't find anything wrong with it." It was required viewing at all the U.S. service academies, college/university Air Force Reserve Officer Training Corps detachments, Air Force Officer Training Schools, the U.S. Navy's former Aviation Officer Candidate School, and the Coast Guard Officer Candidate School, where it was used as a teaching example for the situational leadership theory, although not currently used by the USAF. The film is also widely used in both the military and civilian worlds to teach the principles of leadership. Michael Gebert declares it the best film of 1949. and Christopher Tookey writes, it is "probably the best picture about the pressures which war imposes on those at the top." In its initial release, the film took in $3,225,000 in rentals in the U.S. alone. On the review aggregator website Rotten Tomatoes, 96% of 26 critics' reviews are positive. The website's consensus reads: "Twelve O'Clock High is a high-stakes, high-tension war drama powered by great, well-written characters."