At the time of this production, there was a legal requirement that permission had to be obtained from well-known living public figures to be depicted on film. Several prominent scientists refused permission, including Niels Bohr, Sir James Chadwick and Lise Meitner. This unfortunately gave the film the appearance the Manhattan Project was more all-American than it really was.
This film did poorly at the box office, resulting in a loss to MGM of $1,596,000 (nearly $21M in 2022) according to studio records.
Agnes Moorehead filmed a bit as a German scientist, but it was cut after the producers couldn't get a clearance from the real scientist.
The "thanks" for Tony Owen is for Owen's wife Donna Reed, who shared a finder's fee with her high school science teacher for developing the premise of the film.
Maj. Gen. Leslie Groves, the head of the Manhattan Project, was paid $10,000 to act as a consultant for this film.