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The United States is known to have possessed three types of weapons of mass destruction: nuclear weapons, chemical weapons, and biological weapons. The U.S. is the only country to have used nuclear weapons in combat in the atomic bombings of Hiroshima and Nagasaki in World War II. It had secretly developed the earliest form of the atomic weapon during the 1940s under the title "Manhattan Project".〔(The world's nuclear stockpile ). 7 April 2010.〕 The United States pioneered the development of both the nuclear fission and hydrogen bombs (the latter involving nuclear fusion). It was the world's first and only nuclear power for four years before being joined in the "nuclear club" by the Soviet Union. The United States has the second largest number of deployed nuclear weapons in the world, after Russia. ==Nuclear weapons== (詳細はJapan in World War II in the atomic bombings of Hiroshima and Nagasaki. Altogether, the two bombings killed an estimated 140,000 civilians and military personnel and injured another 130,000. The atomic bombings of Hiroshima and Nagasaki were the first and only time the U.S. employed weapons of mass destruction against an enemy state in warfare. The U.S. conducted an extensive nuclear testing program. 1,054 tests were conducted between 1945 and 1992. The exact number of nuclear devices detonated is unclear because some tests involved multiple devices while a few failed to explode or were designed not to create a nuclear explosion. The last nuclear test by the United States was on September 23, 1992; the U.S. has signed but not ratified the Comprehensive Test Ban Treaty. Currently, the United States nuclear arsenal is deployed in three areas: : * Land-based intercontinental ballistic missiles, or ICBMs; : * Sea-based, nuclear submarine-launched ballistic missiles, or SLBMs; and : * Air-based nuclear weapons of the U.S. Air Force's heavy bomber group The United States is one of the five "Nuclear Weapons States" under the Nuclear Non-Proliferation Treaty, which the U.S. ratified in 1968. On October 13, 1999, the U.S. Senate rejected ratification of the Comprehensive Test Ban Treaty, having previously ratified the Partial Test Ban Treaty in 1963. The U.S. has not, however, tested a nuclear weapon since 1992, though it has tested many non-nuclear components and has developed powerful supercomputers in an attempt to duplicate the knowledge gained from testing without conducting the actual tests themselves. In the early 1990s, the U.S. stopped developing new nuclear weapons and now devotes most of its nuclear efforts into stockpile stewardship, maintaining and dismantling its now-aging arsenal. The administration of George W. Bush decided in 2003 to engage in research towards a new generation of small nuclear weapons, especially "earth penetrators" .〔(BBC NEWS | Americas|Mini-nukes on US agenda )〕 The budget passed by the United States Congress in 2004 eliminated funding for some of this research including the "bunker-busting or earth-penetrating" weapons. The exact number of nuclear weapons possessed by the United States is difficult to determine. Different treaties and organizations have different criteria for reporting nuclear weapons, especially those held in reserve, and those being dismantled or rebuilt: : * As of 1999, the U.S. was said to have 12,000 nuclear weapons of all types stockpiled.〔(Nuclear Forces Guide )〕 : * In its Strategic Arms Reduction Treaty (START) declaration for 2003, the U.S. listed 5968 deployed warheads as defined by START rules.〔()〕 : * For 2007, the Bulletin of the Atomic Scientists listed the U.S. with about 5,400 total nuclear warheads: around 3,575 strategic and 500 nonstrategic warheads; and about 1,260 additional warheads held in the inactive stockpile. Other warheads are in some step of the disassembly process.〔(U.S. nuclear forces, 2008 ) ''The Bulletin of the Atomic Scientists''〕 : * The exact number as of Sept. 30, 2009, was 5,113 warheads, according to a U.S. fact sheet released May 3, 2010.〔 ()"News article 3, May 2010"〕 In 2002, the United States and Russia agreed in the SORT treaty to reduce their deployed stockpiles to not more than 2,200 warheads each. In 2003, the U.S. rejected Russian proposals to further reduce both nation's nuclear stockpiles to 1,500 each.〔(Nuclear Arms Control: The U.S.-Russian Agenda )〕 In 2007, for the first time in 15 years, the United States built new warheads. These replaced some older warheads as part of the Minuteman III upgrade program.〔 2007 also saw the first Minuteman III missiles removed from service as part of the drawdown. Overall, stockpiles and deployment systems continue to decline in number under the terms of the New START treaty. In 2014, Bulletin of the Atomic Scientists released a report, stating that there are a total of 2,530 warheads kept in reserve, and 2,120 actively deployed. Of the warheads actively deployed, the number of strategic warheads rests at 1,920 (subtracting 200 bombs that are "deployed", but are not considered "strategic"). The amount of warheads being actively disabled rests at about 2,700 warheads, which brings the total United States inventory to about 7,400 warheads.〔http://m.bos.sagepub.com/content/70/1/85.full.pdf〕 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「United States and weapons of mass destruction」の詳細全文を読む スポンサード リンク
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