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A nuclear triad refers to the nuclear weapons delivery of a strategic nuclear arsenal which consists of three components, traditionally strategic bombers, intercontinental ballistic missiles (ICBMs), and submarine-launched ballistic missiles (SLBMs). The purpose of having a three-branched nuclear capability is to significantly reduce the possibility that an enemy could destroy all of a nation's nuclear forces in a first-strike attack; this, in turn, ensures a credible threat of a second strike, and thus increases a nation's nuclear deterrence. ==Traditional components== While traditional nuclear strategy holds that a nuclear triad provides the best level of deterrence from attack, in reality, most nuclear powers do not have the military budget to sustain a full triad. Only the United States and Russia have maintained nuclear triads for most of the nuclear age.〔 Both the US and the Soviet Union composed their triads along the same lines, including the following components: #Bomber aircraft capable of delivering nuclear bombs (carrier-based or land-based; usually armed with long-range missiles).〔 #Land-based missiles (MRBMs or ICBMs).〔〔 #Ballistic missile submarines (SSBNs). Nuclear missiles launched from ships or submarines.〔〔 Although in early years the US Navy sea leg was carrier aircraft based with a very short period using sub launched cruise missiles such as the Regulus before SLBMs were ready to be deployed. The triad also gives the commander in chief the flexibility to use different types of weapons for the appropriate strike while also preserving a reserve of nuclear armaments theoretically safe from a counter-force strike: *ICBMs allow for a long-range strike launched from a controlled or friendly environment at a lower cost per delivered warhead and easiest targeting from a surveyed geographic location.〔http://www.heritage.org/research/reports/2012/01/time-to-modernize-and-revitalize-the-nuclear-triad〕 If launched from a fixed position, such as a missile silo, they are vulnerable to a first strike, though their interception once aloft is substantially difficult,〔〔 Some ICBMs are either rail or road mobile. Medium-range ballistic missiles and ground-launched cruise missiles were also assigned for strategic targets based in nations closer to the potential confrontation, but were eventually forbidden by arms control treaty to the US and Russia. *SLBMs, launched from submarines, allow for a greater chance of survival from a first strike, giving the commander a second-strike capability.〔〔 Some long-range submarine-launched cruise missiles are counted towards triad status; this was the first type of submarine-launched strategic second-strike nuclear weapon before ballistic missile submarines became available. A SLBM is the most difficult to get accurate targeting for as it requires obtaining an accurate geographical fix to program targeting data to the missile, the total cost of a SLBM is increased by the cost of the submarine force, large crews. and deterrence patrols.〔http://www.heritage.org/research/reports/2012/01/time-to-modernize-and-revitalize-the-nuclear-triad〕 *Strategic bombers have greater flexibility in their deployment and weaponry. They can serve as both a first- and second-strike weapon. A bomber armed with AGM-129 ACM missiles, for example, could be classified as a first-strike weapon. A number of bombers often with aerial refueling aircraft kept at safe points would constitute a second-strike weapon.〔〔 In some strategic contexts either with nearby potential enemies or with forward basing lighter aircraft can be used on the strategic level as either a first-strike weapon or if dispersed at small airfields or aboard an aircraft carrier can reasonably avoid a counterstrike giving them regional second-strike capacity, aircraft such as the Mirage 2000, F-15E, A-5 Vigilante, Sea Harrier, or FB-111 are or were tasked part or full-time with land or sea-based strategic nuclear attack missions. An aerial refueling fleet supports intercontinental strategic operations both for heavy bombers and smaller aircraft; it also makes possible around the clock airborne standby of bombers and command aircraft making these airborne assets nearly impossible to eliminate in a first strike. Bomber airborne alert patrols are very expensive in terms of fuel and aircraft maintenance, even non-airborne alert basing requires both crew training hours and aircraft upkeep.〔http://www.heritage.org/research/reports/2012/01/time-to-modernize-and-revitalize-the-nuclear-triad〕 Tactical nuclear weapons are used in air, land and sea warfare. Air-to-air missiles and rockets, surface-to-air missiles, and small air-to-ground rockets, bombs, and precision munitions have been developed and deployed with nuclear warheads. Ground forces have included tactical nuclear artillery shells, surface-to-surface rockets, land mines, medium and small man-packable nuclear engineering demolition charges, even man-carried or vehicle-mounted recoilless rifles. Naval forces have carried nuclear-armed naval rocket-assisted and standard depth charges and torpedoes, and naval gunnery shells. Tactical nuclear weapons and the doctrine for their use is primarily for use in a non-strategic warfighting role destroying military forces in the battle area; they are not counted toward triad status despite the possibility of many of these systems being usable as strategic weapons depending on the target. 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「Nuclear triad」の詳細全文を読む スポンサード リンク
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