Castle Bravo was the code name given to the first U.S. test of a dry fuel thermonuclear hydrogen bomb device, detonated on March 1, 1954 at Bikini Atoll, Marshall Islands, as the first test of Operation Castle. Castle Bravo was the most powerful nuclear device ever detonated by the United States (but not the most powerful ever detonated), with a yield of 15 megatons. That yield, far exceeding the expected yield of 4 to 6 megatons, combined with other factors, led to the most significant accidental radiological contamination ever caused by the United States. Fallout from the detonation — intended to be a secret test — poisoned the islanders who had previously inhabited the atoll and returned there afterwards,[1] as well as the crew of Daigo Fukuryū Maru (“Lucky Dragon No. 5”), a Japanese fishing boat, and created international concern about atmospheric thermonuclear testing
Source: Wikipedia
