Castle Bravo

Castle Bravo was the first in a series of high-yield thermonuclear weapon design tests conducted by the United States at Bikini Atoll, Marshall Islands, as part of Operation Castle. Detonated on March 1, 1954, the device was the most powerful nuclear device detonated by the United States and the first lithium deuteride-fueled thermonuclear weapon ever tested using the Teller-Ulam design. Castle Bravo's yield was , 2.5 times the predicted , due to unforeseen additional reactions involving lithium-7, which led to radioactive contamination in the surrounding area. Fallout, the heaviest of which was in the form of pulverized surface coral from the detonation, fell on residents of Rongelap and Utirik atolls, while the more particulate and gaseous fallout spread around the world. The inhabitants of the islands were not evacuated until three days later and suffered radiation sickness. Twenty-three crew members of the Japanese fishing vessel Daigo Fukuryū Maru ("Lucky Dragon No. 5") were also contaminated by the heavy fallout, experiencing acute radiation syndrome. The blast incited a strong international reaction over atmospheric thermonuclear testing. The Bravo Crater is located at . The remains of the Castle Bravo causeway are at . The Castle Bravo device was housed in a cylinder that weighed and measured in length and in diameter. The primary device was a COBRA deuterium-tritium gas-boosted atomic bomb made by Los Alamos Scientific Laboratory, a very compact MK 7 device. This boosted fission device was tested in the Upshot Knothole Climax event and yielded (out of 50–70 kt expected yield range). It was considered successful enough that the planned operation series Domino, designed to explore the same question about a suitable primary for thermonuclear bombs, could be canceled. The implosion system was quite lightweight at , because it eliminated the aluminium pusher shell around the tamper and used the more compact ring lenses, a design feature shared with the Mark 5, 12, 13 and 18 designs.