The plan was audacious, requiring a midnight parachute jump onto a snow-covered mountain plateau, cross-country skiing in subzero temperatures and an assault on an isolated, heavily guarded power plant in southern Norway. And the stakes, though no one in the five-man commando team knew it at the time, were spectacular: Destroy the Nazis' sole source of heavy water, a recently discovered substance that Hitler's scientists were using to try to develop an atomic bomb or risk the creation of a...