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Tethered Bison tube guarded by thorns and barbed wire
Submarines of the United States Navy are built in classes, using a single design for a number of boats. Minor variations occur as improvements are incorporated into the design, so later boats of a class may be more capable than earlier. Also, boats are modified, sometimes extensively, while in service, creating departures from the class standard. However, in general, all boats of a class are noticeably similar.
The Thresher/Permit class of United States Navy nuclear attack submarines was the replacement for the Skipjack class. They were used primarily in the 1960s and 1970s and were replaced by the Sturgeon and Los Angeles classes, and were the result of a study commissioned in 1956 by the Chief of Naval Operations (CNO), Admiral Arleigh Burke. In "Project Nobska," the Committee on Undersea Warfare of the National Academy of Sciences considered the lessons learned from various prototypes and experimental platforms.
The new class kept the proven S5W reactor plant from the immediately preceding Skipjacks, but were a radical change in many other ways. The Threshers had the large bow-mounted sonar and angled, amidships torpedo tubes pioneered by the Tullibee. The use of a new alloy steel, HY-80, increased the boats' test depth, and a redesign of the engineering spaces, with the turbines supported on "rafts" that were suspended from the hull on sound damping isolation mounts. Their hulls were more effectively streamlined and had smaller sails, so while they used the same reactor plant as the Skipjacks, their larger size did not reduce their speed. The ships had torpedo launchers moved to the middle of the hull, so leaving free a lot of space for the huge BQQ-2 sonar system (BQQ-5 with modernized ships), a new and powerful detection low-frequence sensor. Initially they had Mk-37 torpedoes, but later they were replaced with the far better Mk-48 plus UGM-84 Harpoon (4, replacing the same number of Mk-48s) and SUBROC (6, lather reduced to 4 when Harpoon were adopted). The maximum was 23 weapons, or theorically 46 mines (Mk 57, 60 or 67), or a mix of mines, torpedoes and missiles.
The first submarine commissioned in this class was the ill-fated Thresher, and so the class was known by her name. When Thresher was lost, the class took the name of the second ship in the class, Permit, and the SubSafe Program began. SubSafe includes specific training of SubSafe Quality Assurance inspectors in the engineroom crew, and tracks extremely detailed information about every component of a submarine's engineroom that contacts seawater. In addition, joints in any equipment carrying seawater must be welded (not brazed), and every hull penetration larger than a certain size can be quickly shut by a remote hydraulic mechanism.
The engineroom of Jack was lengthened by ten feet to accommodate an experimental direct-drive propulsion system using concentric counter-rotating propellers. Although counter-rotating propellers produced impressive gains in speed on the experimental Albacore, in Jack the results were disappointing.
Flasher, Greenling, and Gato were fitted with heavier machinery and a larger sail, and made ten feet longer than the other units of the class to correct stability problems caused by that weight growth.
General Characteristics
Class and type: Attack submarine
Displacement: Surfaced:3,750tons Submerged: 4,300tons
Length: 278.5ft
Beam: 31.7ft
Propulsion: 1 S5W PWR,2 steam turbines 15,000shp, 1 shaft
Speed Surfaced: 20+knots
Speed Submerged: 30+knots
Range: Unlimited, except by food supplies
Test depth: 400m/1300ft
Complement: 112
Armament: 4xsub harpoon anti ship missile 4-6 SUBROC anti submarine missile, 4x21in amidship tubes (12-18 reloads)
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