The Phantom Empire

Gene Autry plays a singing cowboy of the same name, who runs Radio Ranch, a dude ranch from which he makes a daily live radio broadcast at 2pm. This is a "modern" cowboy story, with planes and such. Gene has two kid sidekicks, Frankie Darro and Betsy King Ross, who lead a club, the "Junior Thunder Riders," in which the kids play at being armoured knights of an unknown civilization, the mysterious Thunder Riders who make a sound like thunder when they ride. The kids, dressing up in capes and water-bucket helmets, play at riding "to the rescue!" (to quote their motto).