Robert Ryan and Richard Brooks--the author of the novel "The Brick Foxhole" on which this film was based--both served in the US Marine Corps during WW II. Ryan asked Brooks that if his book was ever accepted by Hollywood if he would consider Ryan for the unsympathetic role of Montgomery. However, another version of this story maintains that Ryan met Brooks in the library at Camp Pendleton, the California Marine Corps base where they were both stationed and told him he was an actor who was determined to play the movie role of the villain, because, he insisted, "I know that son of a bitch. No one knows him better than I do". Two years later, outside the theater where the film had just previewed, Ryan--who had indeed played the role he had once sought--asked Brooks, "What do you think?".
It has been suggested that one reason the film failed to win any Oscars was due to director Edward Dmytryk and producer Adrian Scott's refusal to testify before the House Un-American Activities Committee (HUAC). Even more, Dmytryk--a Canadian who had become an American citizen only a decade earlier--was one of the notorious anti-HUAC 'Hollywood Ten.' Indeed, subsequent to the HUAC hearings, both Dmytryk and Scott were blacklisted for political reasons and unable to work in Hollywood.
The trivia item below may give away important plot points.
Despite receiving an Academy Award nomination, Robert Ryan rarely talked about his breakthrough role, because he wasn't too happy about the negative aspects of his character, who was a murderous, anti-Semitic psychopath. In real life, Ryan was a committed liberal progressive who detested any forms of bigotry.