Permit-class submarine

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USS Greenling (SS614)
USS Greenling (SSN-614)
Class overview
Builders: Portsmouth Naval Shipyard
Mare Island Naval Shipyard
Ingalls Shipbuilding
New York Shipbuilding
General Dynamics Electric Boat
Operators:  United States Navy
Preceded by: Skipjack-class submarine
Succeeded by: Sturgeon-class submarine
Built: 1958–1967
In commission: 1961–1996
Completed: 14
Lost: 1
Retired: 13
General characteristics
Type: Nuclear submarine
Displacement: 3,750 long tons (3,810 t) surfaced
4,300 long tons (4,369 t) submerged[1]
Length: 278 ft 5 in (84.86 m)
Beam: 31 ft 7 in (9.63 m)
Draft: 25 ft 2 in (7.67 m)
Propulsion: 1 S5W PWR
2 steam turbines, 15,000 shp (11 MW)
1 shaft
Speed: 15 knots (28 km/h; 17 mph) surfaced
28 knots (52 km/h; 32 mph) submerged
Range: Unlimited, except by food supplies
Test depth: 1,300 ft (400 m)
Complement: 112
Sensors and
processing systems:
BQQ-2 sonar (later BQQ-5)
Mark 113 Fire-control system (later Mark 117)
Electronic warfare
and decoys:
Armament: • 4 × 21 in (533 mm) torpedo tubes amidships
• 12-18 × Mark 37 torpedoes, later replaced by Mark 48s
• 4-6 × UUM-44 SUBROC anti-submarine missiles
• 4 × UGM-84 Harpoon anti-ship missiles

The Permit-class submarine, originally known as the Thresher class, was a class of nuclear-powered fast attack submarines (hull classification symbol SSN) in service with the United States Navy from the early 1960s until 1996. They were a significant improvement on the Skipjack class, with greatly improved sonar, diving depth, and silencing.[1] They were the forerunners of all subsequent US Navy SSN designs. They served in the 1960s through middle 1980s, until retired due to age.[2] They were followed by the Sturgeon and Los Angeles classes.

The Thresher class resulted from a study commissioned in 1956 by Chief of Naval Operations (CNO) Admiral Arleigh Burke. In "Project Nobska", the Committee on Undersea Warfare of the United States National Academy of Sciences, collaborating with numerous other agencies, considered the lessons of submarine warfare and anti-submarine warfare 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 sphere and angled, amidships torpedo tubes used in the concurrently-built Tullibee. This placed the sonar sphere in the optimum position for detection of targets at long range. Tullibee was an alternate design optimized for anti-submarine warfare, much smaller and slower than the Threshers and with a quiet turbo-electric propulsion system.[3] Although they used the same HY-80 steel (yield strength 80,000 psi (550 MPa)) as the Skipjacks, the Threshers' pressure hulls were made using an improved design that extended test depth to 1,300 ft. The engineering spaces were also redesigned, with the turbines supported on "rafts" that were suspended from the hull on isolation mounts for acoustic quieting. Drag was reduced, with external fittings kept to a minimum and the sail greatly reduced in size.[1]

The small sail of Thresher (the smallest fitted to an American SSN) compensated for the increased drag of the longer hull, giving Thresher a top speed of 33 knots, the same as the Skipjacks, according to one recollection.[4] However, the small sail had disadvantages as well, including room for only one periscope and a reduced number of electronics masts, less convenient surfaced operation in rough seas, and an increased possibility of "broaching" (inadvertent surfacing) at periscope depth in rough seas.[5]

Only Thresher was fitted with a five-bladed symmetric screw, very similar to the ones originally fitted to the "Skipjacks", which allowed her to reach this speed. During trials of the Skipjack class, it was found that the propeller produced noise below cavitation depth. It was determined that the source of this noise, called blade-rate, was the blades of the screw vibrating when they hit the wake of the sail and control surfaces.[1] This produced a noise that could carry for many miles and could be used by an enemy submarine to set up a firing solution because the frequency of blade-rate was directly related to the speed of the submarine (the RPM of the screw). The solution was to either make the screw smaller so it did not hit the wakes of the sail and control surfaces, which would cavitate more easily because of its increased speed, or have a large screw that gently interacted with these areas of disturbed water. The latter solution was chosen for all subsequent American SSNs. Permit and later submarines of this class had seven-bladed skewback screws, which reduced the problem of blade-rate, but reduced the submarines' top speed to 29-28 knots. Jack was designed with counter-rotating screws, each of which were smaller than the standard seven-bladed screw, as an alternative solution to the blade-rate problem.[1]

The class received mid-life upgrades in the late 1970s and 1980s, including the BQQ-5 sonar suite with a retractable towed array, Mk 117 torpedo fire control equipment, and other electronics upgrades.


The ships had their torpedo tubes moved to the middle of the hull and angled outboard. This made available the required large space in the bow for the BQQ-2 (BQQ-5 as modernized from the late 1970s) sonar sphere, a new and powerful low-frequency detection sensor. Initially armed with Mark 37 torpedoes, by the late 1960s they carried the improved Mark 48 and the nuclear UUM-44 SUBROC short-range anti-submarine missile, replacing up to six Mk-48s. The Threshers were the first class fitted with the Mark 113 fire control system that enabled the use of SUBROC; they were later upgraded with the Mark 117 system. In the late 1970s the UGM-84 Harpoon anti-ship missile was introduced; typically four were carried in place of Mk-48s.

The maximum weapons load was 23 torpedoes/missiles or, theoretically, up to 42 Mk-57, -60, or -67 mines. Any mix of mines, torpedoes, and missiles could be included.[6]


The first submarine commissioned in the class was the ill-fated Thresher, and so the class was known by her name. When Thresher was lost on 10 April 1963, the class took the name of the second ship in the class, Permit. Thresher had numerous advanced design features and embodied the future of US Navy submarine design, and her loss was a serious blow. As a result, the SUBSAFE program was instituted to correct design flaws and introduce strict manufacturing and construction quality control in critical systems. The seawater and main ballast systems of future classes (Sturgeon-class SSNs and Benjamin Franklin-class SSBNs) were redesigned, and some Threshers and other submarines were rebuilt to SUBSAFE standards. SUBSAFE includes specific training of SUBSAFE quality assurance inspectors in the engineering crew, and tracks extremely detailed information about every component of a submarine that is subject to sea pressure. Joints in any equipment carrying seawater must be welded (not brazed), and every hull penetration larger than a specified size can be quickly shut by a remote hydraulic mechanism.[7] The program has been very successful, as no SUBSAFE submarines have been lost as of 2015 (Scorpion was not SUBSAFE).

Flasher, Greenling, and Gato were fitted with a larger sail, to house additional masts, and built ten feet longer than the other units of the class to include more SUBSAFE features, additional reserve buoyancy, more intelligence gathering equipment and improved accommodations. Haddock was completed with the larger sail but the standard 279-foot hull. The Sturgeon class was built with the Flasher-type hull as part of their SUBSAFE redesign, along with an even larger sail.[8]

The engine room 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 because of the difficulty in sealing the shaft. Jack was also used to test polymer ejection that could reduce flow noises that degraded sonar performance.

Ships in class[edit]

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

Name Hull number Builder Laid Down Launched Commissioned Fate
Thresher SSN-593 Portsmouth Naval Shipyard 28 May 1958 9 July 1960 3 August 1961 Lost with 129 crewmembers and shipyard personnel on 10 April 1963, 200 nautical miles (370 km) east of Cape Cod, Massachusetts, exact cause unknown.
Permit SSN-594 Mare Island Naval Shipyard 16 July 1959 1 July 1962 29 May 1962 Decommissioned 12 June 1991, recycled via the nuclear Ship and Submarine Recycling Program 20 May 1993.
Plunger SSN-595 Mare Island Naval Shipyard 2 March 1960 9 December 1961 21 November 1962 Decommissioned 3 January 1990, recycled via the nuclear Ship and Submarine Recycling Program 8 March 1996.
Barb SSN-596 Ingalls Shipbuilding, Pascagoula, Mississippi 9 November 1959 11 Feb 1962 24 August 1963 Decommissioned 20 December 1989, recycled via the nuclear Ship and Submarine Recycling Program 14 March 1996.
Pollack SSN-603 New York Shipbuilding, Camden, New Jersey 14 March 1960 17 March 1962 26 May 1964 Decommissioned 1 March 1989, recycled via the nuclear Ship and Submarine Recycling Program 17 February 1995.
Haddo SSN-604 New York Shipbuilding, Camden, New Jersey 9 September 1960 18 August 1962 16 December 1964 Decommissioned 12 June 1991, recycled via the nuclear Ship and Submarine Recycling Program 20 June 1992.
Jack SSN-605 Portsmouth Naval Shipyard 16 September 1960 24 April 1963 31 March 1967 Decommissioned 11 July 1990, recycled via the nuclear Ship and Submarine Recycling Program 30 June 1992.
Tinosa SSN-606 Portsmouth Naval Shipyard 24 November 1959 9 December 1961 17 October 1964 Decommissioned 15 January 1992, recycled via the nuclear Ship and Submarine Recycling Program 15 August 1992.
Dace SSN-607 Ingalls Shipbuilding, Pascagoula, Mississippi 6 June 1960 18 August 1962 4 April 1964 Decommissioned 2 December 1988, recycled via the nuclear Ship and Submarine Recycling Program 1 January 1997.
Guardfish SSN-612 New York Shipbuilding, Camden, New Jersey 13 February 1961 15 May 1965 20 December 1966 Decommissioned 2 February 1992, recycled via the nuclear Ship and Submarine Recycling Program 9 July 1992.
Flasher SSN-613 Electric Boat 14 April 1961 22 June 1963 22 July 1966 Decommissioned 26 May 1992, recycled via the nuclear Ship and Submarine Recycling Program 11 May 1994.
Greenling SSN-614 Electric Boat 15 August 1961 4 April 1964 3 November 1967 Decommissioned 18 April 1994, recycled via the nuclear Ship and Submarine Recycling Program 30 September 1994.
Gato SSN-615 Electric Boat 15 December 1961 14 May 1964 25 January 1968 Decommissioned 25 April 1996, recycled via the nuclear Ship and Submarine Recycling Program.
Haddock SSN-621 Ingalls Shipbuilding, Pascagoula, Mississippi 24 April 1961 21 May 1966 22 December 1967 Decommissioned 7 April 1993, recycled via the nuclear Ship and Submarine Recycling Program.

See also[edit]


  1. ^ a b c d e Friedman, Norman (1994). U.S. Submarines Since 1945: An Illustrated Design History. Annapolis, Maryland: United States Naval Institute. pp. 141–146, 243. ISBN 1-55750-260-9. 
  2. ^ Friedman, pp. 235-236
  3. ^ Friedman, pp. 136-142, 243
  4. ^ Polmar, Norman; Moore, K. J. (2004) Cold War Submarines: The Design and Construction of U.S. and Soviet Submarines, Potomac Books, p. 363
  5. ^ Friedman, pp. 143-146
  6. ^ War Machines Encyclopedia, Aerospace Publishing Ltd., Italian version printed by De Agostini, p.526-527)
  7. ^ Friedman, pp. 143-146
  8. ^ Friedman, pp. 143-146
  • Gardiner, Robert and Chumbley, Stephen, Conway's all the world's fighting ships 1947-1995, London: Conway Maritime Press, 1995. ISBN 1-55750-132-7.
  • Karam, P. Andrew and Thompson, Roger, Rig Ship for Ultra Quiet: Life on a nuclear attack boat at the end of the Cold War. Google Books link
  • Hutchinson, Robert, Jane's Submarines, War Beneath The Waves, From 1776 To The Present Day, Harper Paperbacks, 2005. ISBN 0-06081-900-6.
  • Polmar, Norman (2004). Cold War Submarines: The Design and Construction of U.S. and Soviet Submarines, 1945-2001. Dulles: Brassey's. ISBN 978-1-57488-594-1.

External links[edit]