Frank Capra began this project but left due to unhappiness with the script (Capra wanted to use his own script but 'John Wayne (I)' insisted that James Edward Grant be brought to rewrite it) and budget.
John Wayne was suffering from the early stages of lung cancer during filming (although he didn't know it at the time). After the near fatal fire scene accident he started having a chronic cough and that night started spitting up spots of blood (he continued to smoke still unaware of the real cause). The intense fire stunt seemed to inflame his condition.
David Niven was originally cast as Cap Carson but left after one of the earlier script rewrites, complaining that it was becoming simply "a typical John Wayne film" and that his role had become smaller. Lloyd Nolan replaced him.
Final movie written by Oscar winner Ben Hecht.
While filming a scene where the main tent catches fire, 'John Wayne' was almost killed when the set collapsed. As he was "fighting" the fire, Wayne was to be cued by the assistant director when to leave before the set was to collapse in flames. Either Wayne didn't hear the cue, or the a.d. mistimed it (it was never determined which), but the flaming set began to collapse before Wayne got out. He escaped with just a few seconds to spare before the entire set would have fallen down on top of him.