On 1 March 1954, the United States carried out its largest ever nuclear test. Named ‘Castle Bravo’, the test was part of a series of similar events, ‘Operation Bravo’, designed to assess the feasibility of high-yield and therefore high-energy devices. ‘Castle Bravo’ was expected to produce a yield of six megatons (375 times larger than the bomb that destroyed Hiroshima) but the scientists involved miscalculated. The actual yield was fifteen megatons, 2.5 times higher than predicted and more than 900 times as powerful as the Hiroshima bomb. Becky Alexis-Martin, author of Disarming Doomsday, describes the test as “the most significant radiological incident in US history.” How so?