William Holden and Richard Widmark became good friends during the production of the film. When Widmark became ill with the flu and was confined to his room, Holden bought him a snare drum because he knew Widmark played the drums. Widmark later remarked, "That four months of being constantly together on a film location was the equivalent of ten or fifteen years of friendship."
Production was shut down for six months when William Holden contracted salmonella poisoning, and the film had to be finished in Hollywood.
This was based upon the actual "Beefsteak Raid" of September 14-16, 1864.
Both William Holden and director Edward Dmytryk were concerned about the script of the film before production even began. At one point during filming, Holden, who was hung-over and dealing with an unruly horse, became angry and tried shoving the script up the horse's rear, yelling, "That's where it belongs!"
Production had to be suspended for a while when Hurricane Betsy passed over Louisiana in mid-September 1965.