To die, espescially in combat; most likely from the idea that a dead soldier's death benifit would serve to pay off his family's morgtage. Often shortened to "bought it."
Chuck Lindberg later recalled the hazards of lugging a tank that carried seventy-two pounds of... napalm... under twelve hundred pounds of pressure... "It was dangerous work. A lot of guys bought the farm trying that."
--James Bradley, in Flags of our Fathers