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SSN-594 Permit class  

Overview 

Specifications
Ships
Sources and Resources

In 1956 Admiral Arleigh Burke, then CNO, requested that the Committee on Undersea Warfare of the National Academy of Sciences to study the effect of advanced technology on submarine warfare. The result of this study, dubbed "Project Nobska" was an increased emphasis on deeper-diving, ultraquiet designs utilizing long-range sonar. The Permit class was based on Project Nobska’s recommendations. Hull streamlining, reduction in sail dimensions by approximately 50%, quieting of the propulsion plant and an increase in test depth all led to a dramatic advance in submarine operational capabilities and stealth.

The SSN-594 Permit class was the world's first modern, quiet, deep-diving fast attack submarines, integrating such advanced features as a hydrodynamically shaped hull, a large bow mounted sonar array, advanced sound-silencing features, and an integrated control/attack center with the proven S5W reactor plant. These submarines were a major advance over previous submarine designs, and established the pattern of all successive American attack submarine classes, in several extremely important respects:

  • They were the first submarines to have hulls constructed of High Yield-80 (HY-80) steel alloy, which allowed operations at substantially greater depths than previous submarines.
  • They were the first submarines to have raft mountings for turbines, motors and other equipment, resulting in substantially quieter operations.
  • They were the first submarines to have a large bow-mounted sonar requiring the installation of torpedo tubes amidships, aft of the forward crew compartment.
Although they were larger than the previous SSN 585 Skipjack class, and used the same nuclear power plant, their hull design did not compromise their underwater speed. Designed for prolonged periods submerged, they were limited only by the amount of food that she can carry, and were capable of sustained operation at high speed.

These submarines were originally designated the THRESHER class, but the USS Thresher (SSN 593) was lost 200 miles off the coast of New England on 10 April 1963. According to investigators, a seawater pipe in the aft engine spaces broke, spraying water into the engine room and shorting one of the main electrical bus boards. The sub lost electrical power and couldn't operate the reactor. Darkness, a sea mist, and sheer terror inhibited the crew from manually actuating the valves. The aft part of the sub filled up with water and tilted down. With no power to get back on line, the sub drifted down to crush depth and imploded. A ghastly death for an entire crew, and one the US Navy vowed never to allow happen again.

The ill-fated USS Thresher (SSN-593) and her crew did not suffer in vain. Out of that terror and the lessons learned grew the SubSafe Program. Through this program, every submarine in the US Fleet, every pressure hull integrity-related system aboard those subs, and every pressure-related part within those systems must be certified as being 100% safe for use on a submarine. The goals are to ensure that in case of a casualty, the ship and its crew can be recovered and to ensure that the integrity of the material used on the ship can operate at design test depth. Directly related to the Thresher tragedy, sea-connected joints can no longer be brazed; they must now be welded. The SubSafe program brought other controls, too. Now when an emergency arises aboard a sub, all vital equipment which sailors would need quick access to in the event of an emergency is clearly marked and easily accessible. At all times an operator is one second away from flipping the emergency main ballast tanks to vent, so the sub can rise to the surface.

The Navy took other steps to ensure such a tragedy never occur again. Following the recommendations of a special Presidential Deep Submergence Review Group, the Deep Submergence Rescue System was developed in the mid-1960s. The deep submergence rescue vehicles Mystic (DSRV 1) and Avalon (DSRV 2) of the Deep Submergence Unit are the genesis of that program.

The last three units of this class [Flasher, Greenling, Gato] were modified during construction to incorporate lessons learned from the loss of the Thresher. Fitted with heavier machinery and a larger sail, they were ten feet longer than the other units of the class to correct stability problems caused by weight growth.

The SSN 605 Jack was fitted with an experimental direct-drive propulsion system coupled with a pair of counter-rotating propellers. The engine spaces were lengthened by ten feet and the shaft was lengthened by seven feet to accomodate this additional equipment. Although counter-rotating propellers had previously produced impressive gains in speed on the experimental Albacore, in this instance the results were disappointing and led to the abandoment of this approach in subsequent submarine design.

Specifications  Return to Top

Displacement 4,200 tons submerged
3,540 tons Light Displacement
Length 278 feet
297 feet SSN-605
292 feet SSN-613-615
Beam 32 feet
Draft 28 ft Maximum Navigational Draft
Speed official - 20-plus knots
actual - 30 knots [35 mph] submerged
actual - 15 knots [17 mph] tactical
Operating Depth official: 400 feet
Actual: 1300 feet [400 meters] test depth
Actual: 1900 feet [600 meters] collapse depth
Construction High Yield-80 (HY-80) steel alloy
Power Plant One S5W nuclear reactor
two steam turbines, one shaft, 15,000 shp
Armament MK 48 Torpedoes, four torpedo tubes
UUM-44A SUBROC
UGM-84A/C Harpoon
MK 57 deep water mines
MK 60 CAPTOR mines
Sensors BQQ-5 bow-mounted sonar
TB-16 Towed Sonar Array
Complement 143
Unit Operating Cost
Annual Average
$10,000,000 [source: [FY1996 VAMOSC]
Builders SSNs 594, 595, Mare Island Naval Shipyard; 596, 607, 621, Ingalls Shipbuilding; 603, 604, 612, New York Shipbuilding; 605, 606, Portsmouth Naval Shipyard; 613-615, General Dynamics' Electric Boat Division

Ships  Return to Top

Name Number Builder Homeport Ordered Commissioned Decommissioned
Thresher SSN-593 Portsmouth NSY Portsmouth 15 Jan 1958 03 Aug 1961 10 Apr 1963
Permit SSN-594 Mare Island NSY San Diego 27 Jan 1958 29 May 1962 23 Jul 1991
Plunger SSN-595 Mare Island NSY   23 Mar 1959 21 Nov 1962 02 Feb 1990
Barb SSN-596 Ingalls   1958 24 Aug 1963 10 Mar 1989
Pollack SSN-603 New York SB   03 Mar 1959 26 May 1964 01 Mar 1989
Haddo SSN-604 New York SB San Diego 03 Mar 1959 16 Dec 1964 12 Jun 1991
Jack SSN-605 Portsmouth NSY New London 13 Mar 1959 31 Mar 1967 11 Jul 1990
Tinosa SSN-606 Portsmouth NSY New London 17 Dec 1958 17 Nov 1964 15 Jan 1992
Dace SSN-607 Ingalls   03 Mar 1959 04 Apr 1964 02 Dec 1988
Guardfish SSN-612 New York SB San Diego 09 Jun 1960 20 Dec 1966 04 Feb 1992
Flasher SSN-613 Electric Boat San Diego 09 Jun 1960 22 Jul 1966 14 Sep 1992
Greenling SSN-614 Electric Boat Portsmouth 09 Jun 1960 03 Nov 1967 18 Apr 1994
Gato SSN-615 Electric Boat New London 09 Jun 1960 25 Jan 1968 25 Apr 1996
Haddock SSN-621 Ingalls Vallejo 24 Aug 1960 22 Dec 1967 07 Apr 1993

Sources and Resources  Return to Top