The day after Johnny Horton's recording of the theme song was released, he was killed in a car crash. Despite the singer not being around to promote the record, it reached #1 on the country charts and #4 on the Hot 100. It also reached #23 in the UK.
Years after the production was first shown in public, the producers of the film admitted that, in the scene where Capucine is trying to laugh, she was actually tickled on her feet and that her laughs and pleas for mercy were entirely genuine.
In the final fight scene you can actually see John Wayne without his wig as he falls backwards after being punched.