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Operation Castle was a United States series of high-yield (high-energy) nuclear tests by Joint Task Force 7 (JTF-7) at Bikini Atoll beginning in March 1954. It followed ''Operation Upshot-Knothole'' and preceded ''Operation Teapot''. Conducted as a joint venture between the Atomic Energy Commission (AEC) and the Department of Defense (DoD), the ultimate objective of the operation was to test designs for an aircraft-deliverable thermonuclear weapon. Operation Castle was considered by government officials to be a success as it proved the feasibility of deployable "dry" fuel designs for thermonuclear weapons. There were technical difficulties with some of the tests: one device had a yield much lower than predicted (a "fizzle"), while two other devices detonated with over twice their predicted yields. One test in particular, ''Castle Bravo'', resulted in extensive radiological contamination of nearby islands (including inhabitants and U.S. soldiers stationed there), as well as a nearby Japanese fishing boat (''Daigo Fukuryū Maru''), resulting in one direct fatality and continued health problems for many of those exposed. Public reaction to the tests and an awareness of the long-range effects of nuclear fallout has been attributed as being part of the motivation for the Partial Test Ban Treaty of 1963. ==Background== Bikini Atoll had previously hosted nuclear testing in 1946 as part of ''Operation Crossroads'' where the world’s fourth and fifth atomic weapons were detonated in Bikini Lagoon. Since then, US nuclear weapons testing had moved to Enewetok Atoll to take advantage of generally larger islands and deeper water. Both Atolls were part of the US Pacific Proving Grounds. The extremely high yields of the Castle weapons caused concern within the AEC that potential damage to the limited infrastructure already established at Eniwetok would delay other operations. Additionally, the cratering from the ''Castle'' weapons was expected to be comparable to that of ''Ivy Mike'', a 10.4 megatons of TNT (Mt) device tested at Eniwetok in 1952 leaving a crater approximately in diameter marking the location of the obliterated test island Elugelab.〔''Operation Ivy'', pg 192〕 The ''Ivy Mike'' test was the world's first "hydrogen bomb", producing a full-scale thermonuclear or fusion explosion. The ''Ivy Mike'' device used liquid deuterium, an isotope of hydrogen, making it a "wet" bomb. The complex dewar mechanisms needed to store the liquid deuterium at cryogenic temperatures made the device three stories tall and 82 tons in total weight, far from being a deliverable weapon.〔''Dark Sun'', pg 495.〕 With the success of ''Ivy Mike'' as proof of the Teller-Ulam bomb concept, research began on using a “dry" fuel to make a practical fusion weapon so that the United States could begin production and deployment of thermonuclear weapons in quantity. The final result incorporated lithium deuteride as the fusion fuel in the Teller-Ulam design, vastly reducing size and weight and simplifying the overall design. ''Operation Castle'' was charted to test four dry fuel designs, two wet bombs, and one smaller device. Approval for ''Operation Castle'' was communicated to JTF-7 by Major General Kenneth D. Nichols, General Manager of the AEC, on 21 January 1954. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Operation Castle」の詳細全文を読む スポンサード リンク
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