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: Fast attack submarine
Displacement: 3,750 long tons (3,810 t) surfaced
4,300 long tons (4,369 t) submerged
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
& 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 1960s until 1996. They replaced the Skipjack class. They were used primarily in the 1960s and 1970s, until replaced by the Sturgeon and Los Angeles classes.

The Permit class resulted from 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 United States 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. Although it used the same HY-80 as the Skipjacks, the Threshers' pressure hulls were made using an improved process 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. 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.[1] 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. According to Norman Friedman, in his book U.S. Submarines Since 1945: An Illustrated Design History, 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. 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.[2]


The ships had their torpedo tubes moved to the middle of the hull. This made available the required large space in the bow for the BQQ-2, BQQ-5 in modernized boats, sonar system, a new and powerful detection low-frequency sensor. Initially armed with Mark 37 torpedoes, they later carried the improved Mark 48, the UGM-84 Harpoon (replacing four of the Mk-48s) and the UUM-44 SUBROC (replacing six Mk-48s, four after Harpoon was adopted). The maximum weapons load was 23 torpedoes/missiles or, theoretically 46 Mk-57, 60 or 67 mines. Or a mix of mines, torpedoes and missiles.[3]


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 engine room crew, and tracks extremely detailed information about every component of a submarine's engine room that contacts seawater. 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.

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.

Flasher, Greenling, and Gato were fitted with heavier machinery and a larger sail, to house additional masts, and made 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.


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.

See also[edit]


  • Robert Hutchinson, Submarines, War Beneath The Waves, From 1776 To The Present Day
  • Norman Polmar, Cold War Submarines: The Design and Construction of U.S. and Soviet Submarines
  • Karam, P. Andrew, Rig Ship for Ultra Quiet: Life on a nuclear attack boat at the end of the Cold War


  1. ^ Polmar, Norman; Moore, K. J. (2004) Cold War Submarines: The Design and Construction of U.S. and Soviet Submarines, Potomac Books, p. 363)
  2. ^ Friedman, Norman (1994) U.S. Submarines Since 1945: An Illustrated Design History,Naval Institute Press, pp. 141-145)
  3. ^ War Machines Encyclopedia, Aerospace Publishing Ltd., Italian version printed by De Agostini is p.526-527)

External links[edit]