FACT SHEET CASTLE was a six-detonation nuclear weapon test series (see table) held at the Atomic Energy Commission's (AEC) Pacific Proving Ground (PPG) in Spring 1954. The PPG consisted principally of Enewetak* and Bikini atolls in the northwestern Marshall Islands in the Central Pacific Ocean. Date Assigned Name Location 1 March BRAVO Bikini; sandspit off Nam Island 15 mT? 27 March ROMEO Bikini; barge in BRAVO crater 11 MT 7 April KOON Bikini; surface of Eneman Island 110 KT 26 April UNION Bikini; barge in lagoon off Iroij Island 6.9 MT 5 May YANKEE Bikini; barge in UNION crater 14 May NECTAR Enewetak; barge in MIKED crater Magnitude 13.5 MT 1.69 MT Notes: 4one kiloton equals the approximate energy release of the explosion of one thousand tons of TNT; one megaton equals the approximate energy release of the explosion of one million tons of TNT. b 10.4-MT IVY series detonation in 1952. HISTORICAL BACKGROUND The CASTLE series was held to test large-yield thermonuclear, or hydrogen, devices. Work on this class of devices had progressed through the GREENHOUSE, GEORGE experimental shot in 1951 and the IVY, MIKE shot of 1952. MIKE was the first device that generated a substantial explosive energy from the fusion, or joining, of hydrogen atoms. These explosive * The spelling of Marshall Island place names has changed in recent years in order to more accurately render the sounds of the Marshall Island names using English spelling. (