Lionel Barrymore was severely disabled by arthritis (clearly visible in his hands) and was confined to a wheelchair, making the scene in which his Mr. Temple character gets up and falls taking a swing at Toots more than a dramatic moment.
In a classic case of a director being emotionally manipulative, John Huston informed Claire Trevor that they were to film her song that very day. Trevor was not a trained singer, and had not even rehearsed the song yet. She also felt very intimidated by the A-list actors seated directly in front of her. The result was a hesitant, nervous, uncomfortable rendition, exactly the feeling Huston was hoping to get.
The character of Gaye Dawn (Claire Trevor) was based on real-life moll Gay Orlova (gangster Lucky Luciano's girlfriend), believed at that time to have been executed by a German firing squad. Orlova survived, however, and was known to be living in Paris as late as 1954, trying to join Luciano in Italy.
In the film, James Temple describes the 1935 hurricane that devastated Matacumbe Key. This was one of worst hurricanes in U.S. history and many of the victims of the storm were World War I veterans who were building the Florida Keys portion of U.S. Highway 1, also known as the Overseas Highway. A portion of the highway is seen in the film's opening. The storm also produced the lowest-ever recorded barometric pressure over land in the North American continent.
The ramshackle hotel where most of the drama unfolds was constructed on the Warner Bros. lot along with the beach area. Exterior shots of the hurricane were actually taken from stock footage used in Night Unto Night (1949), a Ronald Reagan melodrama made the same year at Warner Bros.
The main character, Frank McCloud, describes having served with Nora's late husband in the WWII battle at San Pietro, Italy; director/co-screenwriter John Huston had been involved in that battle as the creator of the documentary film San Pietro (1945) while he was in the U.S. Army's motion picture unit.
The character of Johnny Rocco was modeled on Al Capone, who retired to Florida and died there of complications due to advanced syphilis a year before this film was produced. Screenwriter Richard Brooks later revealed he had also incorporated biographical details about another famous gangster, Lucky Luciano, into Rocco's character as well.
While most of the film was shot in Los Angeles, the exterior shots were shot at the Caribbean Club at Mile Marker 105 on US 1. While the property is still there, much of the old exterior was destroyed in a pair of fires.
The film version of "Key Largo" has very little to do with Maxwell Anderson's original play. All the characters in the play had their names changed in the film version. This was very unusual for a play written by Anderson, who was then one of the most highly regarded American playwrights, and whose best-known plays had, on the whole, been filmed faithfully.
This movie was based on Maxwell Anderson's popular Broadway play which featured Paul Muni in the lead role as a fatalistic ex-member of the Loyalist Army who has returned from the Spanish Civil War. For the film version, the time period and the setting were changed. Director John Huston and screenwriter Richard Brooks rewrote the main character, Frank McCloud, making him a World War II veteran who had served in the Italian campaign. The two writers emphasized the idealism of the early Franklin D. Roosevelt years and how those ideals began to erode as organized crime spread through urban areas.
The film was produced in 1948, the same year in which there actually were two major hurricanes, late in the season, less than a month apart, that went directly through the Florida Keys. (See Hurricanes #7 and #8 of 1948)
The original Broadway production of "Key Largo" by Maxwell Anderson opened at the Ethel Barrymore Theater on November 27, 1939 and ran for 105 performances. The original stage cast includes Paul Muni, Uta Hagen and the Broadway debut of character actor James Gregory.