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SSN-594 Permit class

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:

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.


Displacement 4,200 tons submerged
3,540 tons Light Displacement
Length278 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
ArmamentMK 48 Torpedoes, four torpedo tubes
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


Name Number Builder Homeport Ordered Commissioned Decommissioned
Thresher SSN-593Portsmouth NSYPortsmouth15 Jan 195803 Aug 196110 Apr 1963
Permit SSN-594Mare Island NSYSan Diego27 Jan 195829 May 196223 Jul 1991
PlungerSSN-595Mare Island NSY23 Mar 195921 Nov 196202 Feb 1990
BarbSSN-596Ingalls 195824 Aug 196310 Mar 1989
PollackSSN-603New York SB03 Mar 195926 May 196401 Mar 1989
HaddoSSN-604New York SBSan Diego03 Mar 195916 Dec 196412 Jun 1991
JackSSN-605Portsmouth NSYNew London13 Mar 195931 Mar 196711 Jul 1990
Tinosa SSN-606Portsmouth NSYNew London17 Dec 195817 Nov 196415 Jan 1992
DaceSSN-607Ingalls 03 Mar 195904 Apr 196402 Dec 1988
Guardfish SSN-612New York SBSan Diego09 Jun 196020 Dec 196604 Feb 1992
Flasher SSN-613Electric Boat San Diego09 Jun 196022 Jul 199614 Sep 1992
Greenling SSN-614Electric Boat Portsmouth09 Jun 196003 Nov 196718 Apr 1994
Gato SSN-615Electric Boat New London09 Jun 196025 Jan 196825 Apr 1996
Haddock SSN-621Ingalls Vallejo24 Aug 196022 Dec 196707 Apr 1993

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Maintained by Robert Sherman
Originally created by John Pike
Updated Tuesday, October 26, 1999 1:38:04 PM