The opening credits of the viewed film were preceded by a mock newsreel, in which Hume Cronyn, Brian Donlevy and other actors, portraying their characters from the film, are seen burying a time capsule commemorating the discovery of atomic power. The onscreen credits contain the following written statement: "With acknowledgment to Mr. Tony Owen for his cooperation." Many of the individuals depicted in the film were well-known government figures and scientists who were directly or indirectly involved in the production of the atomic bomb during World War II. Among those portrayed were Harry S. Truman, president of the United States at the time of the bombing of Hiroshima, Japan; Major General Leslie R. Groves, head of the atomic bomb project; J. Robert Oppenheimer, head of the team of scientists who developed the bomb; and Secretary of War Henry Stimson. According to a pre-production HR news item, M-G-M consulted with Groves, Oppenheimer and Truman during the preparation of the film. Major Charles Sweeney, the pilot of the airplane that dropped the atomic bomb on Nagasaki, Japan, was commissioned by M-G-M to serve as a military technical advisor.
       HR news items in Dec 1945 and Jan 1946 indicate that M-G-M, Paramount and Twentieth Century-Fox were engaged in a race to be the first studio to produce a motion picture about the atomic bomb. M-G-M gave the picture top priority, and had story writer Robert Considine rush pages of his treatment, as he completed them, to the studio script writers. A Mar 1946 HR news item noted that producer Hal Wallis, who was preparing a $1,500,000 atomic picture entitled Top Secret for Paramount, agreed to cancel his film, merge his story property with M-G-M's and serve as an advisor on the M-G-M picture. Wallis, the first to enter the atomic picture race. negotiated an initial payment plus a substantial gross percentage of the picture's profits in exchange for his story material and research.
       A Dec 1945 HR news item noted that M-G-M stars Spencer Tracy, Clark Gable and Van Johnson were "being groomed for roles" in the film. According to various HR news items in Jun 1946, a controversy erupted when former First Lady Eleanor Roosevelt objected to the casting of Lionel Barrymore as Franklin D. Roosevelt, alleging that the actor had made disparaging remarks about the late president. Production on the film had already begun when the studio decided to hold up Barrymore's scenes until Mrs. Roosevelt had the opportunity to respond to a letter from Barrymore, in which he explained his political statements. Though Barrymore claimed that his remarks were misinterpreted, the Roosevelt family continued to disapprove of the casting and M-G-M replaced him with Godfrey Tearle. A Dec 1945 HR news item noted that M-G-M consulted with Archbishop Francis J. Spellman of New York, who offered a special Mass on the the island of Tinian for American crew members who were assigned to bomb Hiroshima and Nagasaki.
       Although contemporary sources indicate that Leon Ames and Agnes Moorehead were cast, they did not appear in the released film. A pre-production HR news item reported that actor Redmond Doms had been set for a role, but his appearance in the final film has not been confirmed. The film marked the motion picture debut of Guy Williams, who played the title character in the Walt Disney television series Zorro (1957-1959), as well as "Professor John Robinson" in the series Lost in Space (1965-1968). According to a Jul 1946 HR news item, nine of the men who portrayed crew members of the "Enola Gay" were actual World War II veterans. Contemporary sources note that some filming took place in Fort Worth, TX; Los Alamos, NM; Oak Ridge, TN; and at various university campuses. An Oct 1946 HR news item indicates that the release of the film, originally set for Oct 1946, was postponed as a result of M-G-M studio head Louis B. Mayer's decision to add to the film actual footage of the bombing of Hiroshima.