Some of the First Doctor serials, starring William Hartnell, took place in real historical settings. "The Gunfighters" was one such serial, taking place right before the Gunfight at the O.K Corral. Now, being a low budget production, they couldn't afford to fly over to America, or even hire American(or failing that, Canadian)actors. So they did the very best they could, with what they had. So you get this mix of accents which are almost passable, to downright hillarious. The actor playing Billy Clanton, who was a Texan, just said "Fuck it!", delivering his lines in what I can only assume, is his native Cockney accent “Oy ain’t scared of Doc ‘oliday!”.
Aside from the laughable accents, and some glaring historical inaccuracies, Like Johnny Ringo inexplicably being at the, and a casualty of, the eventual shootout, it was a pretty good serial, considering when it was made. It's one of the better stories that doesn't involve aliens, or monsters, or exotic far off worlds. Its a story of the Doctor and his Companions being stuck in the middle of the shit getting ready to hit the fan, then inexplicably deciding to stick around for a while.