Permit-class submarine


The Permit-class submarine was a class of nuclear-powered fast attack submarines in service with the United States Navy from the early 1960s until 1996. They were a significant improvement on the, with greatly improved sonar, diving depth, and silencing. They were the forerunners of all subsequent US Navy SSN designs. They served from the 1960s through to the early 1990s, where they were decommissioned due to age. They were followed by the and classes.
The Thresher class resulted from a study commissioned in 1956 by Chief of Naval Operations 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.

Design

The new class kept the proven S5W reactor plant from the immediately preceding s, 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. 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. Although they used the same HY-80 steel as the Skipjacks, the Threshers pressure hulls were made using an improved design that extended test depth to. 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.
The small sail of Thresher compensated for the increased drag of the longer hull, giving Thresher a top speed of, the same as the Skipjacks, according to one recollection. 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" at periscope depth in rough seas.
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. 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 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. 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.
The class received mid-life upgrades in the late 1970s and 1980s, including the sonar suite with a retractable towed array, Mk 117 torpedo fire control equipment, and other electronics upgrades.

Armament

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 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, Mk 60, or Mk 67 mines. Any mix of mines, torpedoes, and missiles could be included.

Construction

The first submarine commissioned in the class was the ill-fated, 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,. 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 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, and every hull penetration larger than a specified size can be quickly shut by a remote hydraulic mechanism. The program has been very successful, as no SUBSAFE submarines have been lost as of 2019.
,, and 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. was completed with the larger sail but the standard hull. The Sturgeon class was built with the Flasher-type hull as part of their SUBSAFE redesign, along with an even larger sail.
The engine room of was lengthened by 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, 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

The gaps in the hull number sequence were taken by the unique, and the,, and fleet ballistic missile submarine classes.
NameHull numberBuilderLaid DownLaunchedCommissionedFate
SSN-593Portsmouth Naval Shipyard28 May 19589 July 19603 August 1961Lost with 129 crewmembers and shipyard personnel on 10 April 1963, east of Cape Cod, Massachusetts, exact cause unknown.
SSN-594Mare Island Naval Shipyard16 July 19591 July 196229 May 1962Decommissioned 12 June 1991, recycled via the nuclear Ship and Submarine Recycling Program 20 May 1993.
SSN-595Mare Island Naval Shipyard2 March 19609 December 196121 November 1962Decommissioned 3 January 1990, recycled via the nuclear Ship and Submarine Recycling Program 8 March 1996.
SSN-596Ingalls Shipbuilding, Pascagoula, Mississippi9 November 195911 Feb 196224 August 1963Decommissioned 20 December 1989, recycled via the nuclear Ship and Submarine Recycling Program 14 March 1996.
SSN-603New York Shipbuilding, Camden, New Jersey14 March 196017 March 196226 May 1964Decommissioned 1 March 1989, recycled via the nuclear Ship and Submarine Recycling Program 17 February 1995.
SSN-604New York Shipbuilding, Camden, New Jersey9 September 196018 August 196216 December 1964Decommissioned 12 June 1991, recycled via the nuclear Ship and Submarine Recycling Program 20 June 1992.
SSN-605Portsmouth Naval Shipyard16 September 196024 April 196331 March 1967Decommissioned 11 July 1990, recycled via the nuclear Ship and Submarine Recycling Program 30 June 1992.
SSN-606Portsmouth Naval Shipyard24 November 19599 December 196117 October 1964Decommissioned 15 January 1992, recycled via the nuclear Ship and Submarine Recycling Program 15 August 1992.
SSN-607Ingalls Shipbuilding, Pascagoula, Mississippi6 June 196018 August 19624 April 1964Decommissioned 2 December 1988, recycled via the nuclear Ship and Submarine Recycling Program 1 January 1997.
SSN-612New York Shipbuilding, Camden, New Jersey13 February 196115 May 196520 December 1966Decommissioned 2 February 1992, recycled via the nuclear Ship and Submarine Recycling Program 9 July 1992.
SSN-613Electric Boat14 April 196122 June 196322 July 1966Decommissioned 26 May 1992, recycled via the nuclear Ship and Submarine Recycling Program 11 May 1994.
SSN-614Electric Boat15 August 19614 April 19643 November 1967Decommissioned 18 April 1994, recycled via the nuclear Ship and Submarine Recycling Program 30 September 1994.
SSN-615Electric Boat15 December 196114 May 196425 January 1968Decommissioned 25 April 1996, recycled via the nuclear Ship and Submarine Recycling Program.
SSN-621Ingalls Shipbuilding, Pascagoula, Mississippi24 April 196121 May 196622 December 1967Decommissioned 7 April 1993, recycled via the nuclear Ship and Submarine Recycling Program.