Because of new union laws, producers were forced to use regular screen extras without stunt experience. In the opening days of shooting 80 were injured and 3 were killed. The filming of the "Last Stand" sequence from this movie involved some 200 horsemen charging around in pretend battle and was so dangerous that one day during filming Anthony Quinn, who played Crazy Horse, arranged as a gag for a hearse to show up at the filming location.
According to "The Guinness Book of Movie Facts and Feats", three men were killed during the cavalry charge scene. Bill Mead's horse tripped while riding alongside Errol Flynn. As he was going down, the stuntman had the presence of mind to throw his sword forward to avoid it, but bad luck caused the hilt to get stuck in the ground and Mead fell on it, impaling himself.
The highest regular Army rank attained by Winfield Scott was actually Major General. Lieutenant General was a brevet (temporary) rank. The first regular Lieutenant General would be Ulysses S. Grant, promoted to the rank in March of 1864. Gem/ Scott was also one of three veterans of the War of 1812 who was still listed on the rolls of the regular Army at the start of the Civil War.
In the montage of battle scenes that show the 7th Cavalry taming the frontier when they operated out of Fort Abraham Lincoln are several shots of them that will be repeated during the Little Big Horn battle.
The final scene Errol Flynn and Olivia de Havilland filmed was NOT their final scene in the film. According to the daily production notes in the Warner Bros. Archives it was their kissing scene on the Bacon veranda.
Hollywood legend has it that director Raoul Walsh had an inspired choice to play Sitting Bull....Buster Keaton. He approached Jack Warner with the idea and Warner replied " Custer beaten by Buster Keaton?", and that was the end of that!