This is one of my favorite roles - second to Ethan Edwards in "The Searchers" - I cannot for the LIFE of me figure out how people can actually keep a straight face and say that John Wayne had no range as an actor. He was COMPLETELY believable as Captain Nathan Brittles, even though the Duke was 42 playing about 65!
The mutual respect and affection between he and "Quincannon" was INCREDIBLY good acting, and showed the comfort level that existed between the two actors.