Sixty-one years ago on an island in the South Pacific, scientists and military officers, fishermen and Marshall Islands natives observed first-hand what Armageddon would be like. And it almost killed them all. The Atomic Energy Commission code-named the nuclear test Castle Bravo. The March 1, 1954 experiment was the first thermonuclear explosion based on practical technology that would lead to a deliverable H-bomb for the Air Force’s Strategic Air Command—part of the Operation Castle series of tests needed to manufacture the high-yield weapons. Bravo was the worst radiological disaster in American atomic testing history—but the test provided information that led...