Castle Bravo was the code name given to the first United States test of a dry fuel 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 Tsar Bomba, the most powerful device ever detonated), with a yield of 15 megatons of TNT.