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Thresher/Permit class attack submarine
Class Overview
Class Type	Attack Submarine
Class Name	Thresher Shark/Permit (a food fish)
Preceded By	Skipjack-class attack submarine USS Triton USS Halibut
Succeeded By	Chronologically: USS Tullibee George Washington-class ballistic missile submarine By Type: Sturgeon-class attack submarine
Ships of the Class:	Thresher, Permit, Plunger, Barb, Pollack, Haddo, Jack, Tinosa, Dace, Gaurdfish, Flasher, Greenling, Gato, Haddock

The Thresher/Permit class of United States Navy submarines was 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 USS Tullibee (SSN-597). 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 first submarine commissioned in this class was the ill-fated Thresher (SSN-593), 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 (SSN-594), 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 (SSN-605) 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 (AGSS-569), in Jack the results were disappointing.

Flasher (SSN-613), Greenling (SSN-614), and Gato (SSN-615) 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.

• Displacement: 4200 tons submerged, 3540 tons light
• Length: 278 feet, except SSN-605: 297 feet and SSN-613–615: 292 feet
• Beam: 32 feet
• Draft: 28 feet
• Speed: 30 knots
• Depth: 400 meters (1300 feet)
• Powerplant: S5W reactor
• Armament: four 21-inch torpedo tubes
• Complement: 143 officers and men

The gaps in the hull-number sequence were taken by the unique Tullibee (SSN-597), and the George Washington, Ethan Allen, and Lafayette fleet ballistic missile submarine classes.

• Thresher (SSN-593)
• Permit (SSN-594)
• Plunger (SSN-595)
• Barb (SSN-596)
• Pollack (SSN-603)
• Haddo (SSN-604)
• Jack (SSN-605)
• Tinosa (SSN-606)
• Dace (SSN-607)
• Guardfish (SSN-612)
• Flasher (SSN-613)
• Greenling (SSN-614)
• Gato (SSN-615)
• Haddock (SSN-621)

• General Dynamics - Principle class design manufacturer.

Wikimedia Commons has media related to:

Thresher/Permit class submarines

• SSN-594 Permit class at GlobalSecurity.org