Castle Bravo was the coe name given to the first U.S. test of a so-called dry fuel thermonuclear (fusion- rather than fission-based) device, detonated on March 1, 1954 at Bikini Atoll, Marshall Islands, by the United States, as the first test of Operation Castle (a longer series of tests of various devices). Fallout from the detonation—intended to be a secret test—poisoned the crew of Daigo Fukuryū Maru ("Lucky Dragon No. 5"), a Japanese fishing boat, and created international concern about atmospheric thermonuclear testing.