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Named after its lead boat, the of nuclear-powered submarines is, , serving with its sole operator, the United States Navy. Fourteen of the eighteen boats are ballistic missile submarines (SSBN), which, along with U.S. Air Force strategic bombers and intercontinental ballistic missiles, constitute the nuclear-deterrent triad of the U.S.〔Chinworth 2006, p. 2.〕 The remaining four have been converted from their initial roles as SSBNs to cruise-missile carriers (SSGN). The ''Ohio''-class boats, each displacing 18,750 tons submerged, are the third largest submarines in the world, behind the 48,000-ton Typhoon class and 24,000-ton ''Borei'' class of the Russian Navy. The ''Ohio'' class replaced the ''Benjamin Franklin''- and ''Lafayette''-class SSBNs.〔 The ''Ohio'' class was designed in the 1970s to carry the concurrently-designed Trident submarine-launched ballistic missile. Both variants of the Tridents—the UGM-96 Trident I and the UGM-133 Trident II—are propelled by three-stage solid propellant rockets and are equipped with 8–14 nuclear warheads.〔 The 73,000 lb (33,100 kg) UGM-96, with a range of 4,000 mi (6,400 km), served from October 1979, starting with the ''Benjamin Franklin''-class USS ''Francis Scott Key'', until 2006.〔Chant 2005, pp. 42–43.〕 The 130,000 lb (59,000 kg) UGM-133, with a range of 6,000 mi (9,700 km), is in service , having been introduced in 1990 with USS ''Tennessee''.〔〔 The primary self-defense weapon of the class is the Mk 48 ADCAP torpedo.〔Chant 2005, p. 33.〕 ''Ohio''-class submarines that carry ballistic missiles receive orders from the United States Strategic Command based in Nebraska.〔Genat and Genat 1997, p. 39.〕 In 1994, the Nuclear Posture Review study determined that, of the 18 ''Ohio'' SSBNs the U.S. Navy would be operating in total, 14 would be sufficient for the strategic needs of the U.S. The decision was made to convert four ''Ohio''-class boats into SSGNs capable of conducting conventional land attack and special operations. As a result, the four oldest boats of the class—''Ohio'', ''Michigan'', ''Florida'', and ''Georgia''—progressively entered the conversion process in late 2002 and were returned to active service by 2008. The boats could thereafter carry 154 Tomahawk cruise missiles and 66 special operations personnel, among other capabilities and upgrades.〔 The cost to refit the four boats was around US$1 billion (2008 dollars) per vessel.〔 With the first retirement of an ''Ohio''-class boat scheduled for 2029, the U.S. Navy is currently, , undertaking a program tentatively named SSBN-X to study the prospective replacement of the class. ==Boats== In July 1974, General Dynamics Electric Boat was awarded the contract to construct the ''Ohio''-class submarines.〔 The first of the class, USS ''Ohio'', was laid down in 1976. Due to an unspecified "series of unfortunate problems in Washington D.C."〔 and manufacturing issues, ''Ohio'' did not initiate sea trials until June 1981, setting back the boat's commissioning date to November that year, three years behind schedule.〔 Originally, it was decided that 20 boats were to be built, but due to the 1991 START I agreement between the U.S. and Soviet Union, the U.S. agreed to reduce the number of nuclear warheads it could deploy, and thus rationalized its order to 18 boats.〔Chinworth 2006, p. 3.〕 The last boat of the class, USS ''Louisiana'', was commissioned in September 1997,〔 nearly 16 years after the class entered operational service. Originally designed for 30-year service lives, it was later decided that ''Ohio''-class submarines would each serve for 42 years, comprising two periods of 20 years of operations and a two-year mid-life nuclear refueling. 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「List of Ohio-class submarines」の詳細全文を読む スポンサード リンク
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