The gunfight in the saloon is based on an actual gunfight that took place in the Lady Gay Saloon in Sweetwater, Texas on January 24th, 1876. The shootout involved Bat Masterson, a soldier known as Sergeant Melvin A. King (who was in reality a Corporal) and a woman named Mollie Brennan. King's character in this movie was Sgt. Ernie King, played by Charles Horvath and Mollie Brennan's character was Mollie Day, played by Kasey Rogers.
McCrea had intended for this to be his last film before retiring, and he remarked, "I've never been in a film that lost money."
The opening gunfight takes place in a different (and real) Kansas town, Hays City. The climactic gunfight takes place in Dodge City and is strikingly similar to the opening in Gunsmoke (1955).
Bat Masterson was a featured character in many other Western movies, including the 1947 RKO film "Trail Street", starring Randolph Scott and Robert Ryan, directed by Ray Enright; Columbia's 1955 film "Masterson of Kansas", starring George Montgomery and Nancy Gates, directed by William Castle; Paramount's 1957 film "Gunfight at the O.K. Corral", starring Burt Lancaster and Kirk Douglas, directed by John Sturges; and the television series "Bat Masterson", which ran from 1959 to 1961, and starred Gene Barry as the lawman.
Canadian-born William Barclay "Bat" Masterson (1853-1921) was a buffalo hunter and Indian scout in Dodge City, Kansas while also intermittently serving as the Ford County sheriff (from 1877-79) and a deputy U.S. marshal (1879). He made his living mostly as a saloon keeper and gambler. His brothers, Ed and James Masterson, were also Dodge City lawmen.