On the eve of the 50th anniversary of the world’s biggest bomb blast, this documentary draws on new forensic investigation and meteorological analyses to reveal the true story behind the Cold War race to build the world's most powerful weapon. After Hiroshima and Nagasaki, the United States led the way - but then left the field clear for the Soviet Union to set off the world’s biggest ever explosion,which took place on October 30th, 1961. Along the way billions of dollars and roubles were spent, Pacific islanders were driven from their homes, and military and civilians alike were unwittingly exposed to huge doses of radiation. With first-hand testimony from American eyewitnesses and inhabitants of the islands, and modern scientific forensics, it is revealed for the first time what happened and the real reasons why the US scientists misjudged the potential power behind their early H bomb tests, resulting in three small islands being vaporised and severe radioactive fallout spreading over nearby inhabited islands.