NAZI scientists relied on heavy water to produce the right uranium isotope for an atomic weapon.  They produced most of their heavy water at a hydroelectric in occupied Norway called Vemork.  In February 1943, a small group of Norwegian commandos slipped into Vemork, blew it up, and made their escape.  This is after months of reconnaissance and preparation in the frozen wilderness.  Neal Bascomb tells the story in “The Winter Fortress.”