Rio Grande

Lt. Col. Kirby Yorke (John Wayne) is posted on the Texas frontier to defend settlers against marauding Apaches. His son, Trooper Jeff Yorke (Claude Jarman Jr.), joins the regiment after years of estrangement from his father. The Apaches attack the fort, and Yorke's patrol reaches the Rio Grande, where he meets a Mexican lieutenant who confirms that US troops cannot cross into Mexico.