During the Sixties and Seventies, John Wayne was riddled with ill health.
The hard-drinking, chain-smoking star had a cancerous lung removed back in 1964 and would secretly rely on an oxygen mask on movie sets, especially if at high altitudes.
By 1973, he was 65 and filming one of his last Westerns, Cahill US Marshall, but was suffering from emphysema on his single lung.
Being significantly weakened, Wayne was forced to use a stepladder to climb onto his horse in the movie.
As for riding shots from a distance, Duke’s Cahill had to be doubled by Chuck Roberson.