Castle Bravo

Castle Bravo was the code name given to the first United States test of a dry fuel thermonuclear hydrogen bomb, 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 (and just under one-third the energy of the most powerful ever detonated), with a yield of 15 megatons of TNT. 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 some of the islanders upon their return, 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.