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Operation Crossroads was a pair of nuclear weapon tests conducted by the United States at Bikini Atoll in mid-1946. They were the first nuclear weapon tests since Trinity in July 1945, and the first detonations of nuclear devices since the atomic bombing of Nagasaki on August 9, 1945. The purpose of the tests was to investigate the effect of nuclear weapons on warships. The Crossroads tests were the first of many nuclear tests held in the Marshall Islands, and the first to be publicly announced beforehand and observed by an invited audience, including a large press corps. They were conducted by Joint Army/Navy Task Force One, headed by Vice Admiral William H. P. Blandy, rather than by the Manhattan Project, which had developed nuclear weapons during World War II. A fleet of 95 target ships was assembled in Bikini Lagoon and hit with two detonations of Fat Man plutonium implosion-type nuclear weapons of the kind dropped on Nagasaki, each with a yield of . The first test was ''Able''. The bomb, named ''Gilda'' after Rita Hayworth's character in the 1946 eponymous film, was dropped from the B-29 Superfortress ''Dave's Dream'' of the 509th Bombardment Group on July 1, 1946, and detonated above the target fleet. It caused less than the expected amount of ship damage because it missed its aim point by . The second test was ''Baker''. The bomb, known as ''Helen of Bikini'', was detonated underwater on July 25, 1946. Radioactive sea spray caused extensive contamination. A third deep water test, ''Charlie'', planned for 1947, was canceled primarily because of the United States Navy's inability to decontaminate the target ships after the ''Baker'' test. Ultimately, only nine target ships were able to be scrapped rather than scuttled. ''Charlie'' was rescheduled as Operation Wigwam, a deep water shot conducted in 1955 off the California coast. Bikini's native residents agreed to evacuate the island, with most moving to the Rongerik Atoll. Later, in the 1950s, a series of large thermonuclear tests rendered Bikini unfit for subsistence farming and fishing. Because of radioactive contamination, Bikini remains uninhabited , though it is occasionally visited by sport divers. Although planners attempted to protect participants in the Operation Crossroads tests against radiation sickness, one study showed that the life expectancy of participants was reduced by an average of three months. The ''Baker'' test's radioactive contamination of all the target ships was the first case of immediate, concentrated radioactive fallout from a nuclear explosion. Chemist Glenn T. Seaborg, the longest-serving chairman of the Atomic Energy Commission, called ''Baker'' "the world's first nuclear disaster." ==Background== The first proposal to test nuclear weapons against naval warships was made on August 16, 1945, by Lewis Strauss, future chairman of the Atomic Energy Commission. In an internal memo to Secretary of the Navy James Forrestal, Strauss argued, "If such a test is not made, there will be loose talk to the effect that the fleet is obsolete in the face of this new weapon and this will militate against appropriations to preserve a postwar Navy of the size now planned."〔.〕 With very few bombs available, he suggested a large number of targets widely dispersed over a large area. A quarter century earlier, in 1921, the Navy had suffered a public relations disaster when General Billy Mitchell's bombers sank every target ship the Navy provided for the Project B ship-versus-bomb tests.〔.〕 The Strauss test would be designed to demonstrate ship survivability.〔.〕 Nine days later, Senator Brien McMahon, who within a year would write the Atomic Energy Act and organize and chair the Congressional Joint Committee on Atomic Energy, made the first public proposal for such a test, but one designed to demonstrate the vulnerability, rather than survivability, of ships. He proposed dropping an atomic bomb on captured Japanese ships and suggested, "The resulting explosion should prove to us just how effective the atomic bomb is when used against the giant naval ships."〔.〕 On September 19, the Chief of the United States Army Air Forces (USAAF), General of the Army Henry H. Arnold, asked the Navy to set aside ten of the thirty-eight captured Japanese ships for use in the test proposed by McMahon.〔.〕 Meanwhile, the Navy proceeded with its own plan, which was revealed at a press conference on October 27 by the Commander in Chief, United States Fleet, Fleet Admiral Ernest King. It involved between 80 and 100 target ships, most of them surplus U.S. ships.〔 As the Army and the Navy maneuvered for control of the tests, Assistant Secretary of War Howard C. Peterson observed, "To the public, the test looms as one in which the future of the Navy is at stake ... if the Navy withstands (tests ) better than the public imagines it will, in the public mind the Navy will have 'won.〔, quoted in .〕 The Army's candidate to direct the tests, Major General Leslie Groves, head of the Manhattan Project which built the bombs, did not get the job. The Joint Chiefs of Staff decided that because the Navy was contributing the most men and materiel, the test should be headed by a naval officer. Commodore William S. "Deak" Parsons was a naval officer who had worked on the Manhattan Project and participated in the bombing of Hiroshima. He was now the assistant to the Deputy Chief of Naval Operations for Special Weapons, Vice Admiral William H. P. Blandy, whom he proposed for the role. This recommendation was accepted, and on January 11, 1946, President Harry S. Truman appointed Blandy as head of Army/Navy Joint Task Force One (JTF-1), which was created to conduct the tests. Parsons became Deputy Task Force Commander for Technical Direction. USAAF Major General William E. Kepner was Deputy Task Force Commander for Aviation. Blandy codenamed the tests Operation Crossroads.〔.〕〔.〕 Under pressure from the Army, Blandy agreed to crowd more ships into the immediate target area than the Navy wanted, but he refused USAAF Major General Curtis LeMay's demand that "every ship must have a full loading of oil, ammunition, and fuel."〔.〕 Blandy's argument was that fires and internal explosions might sink ships that would otherwise remain afloat and be available for damage evaluation. When Blandy proposed an all-Navy board to evaluate the results, Senator McMahon complained to Truman that the Navy should not be "solely responsible for conducting operations which might well indeed determine its very existence."〔.〕 Truman acknowledged that "reports were getting around that these tests were not going to be entirely on the level." He imposed a civilian review panel on Operation Crossroads to "convince the public it was objective."〔.〕 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 Crossroads」の詳細全文を読む スポンサード リンク
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