Thresher/Permit-class submarine

Thresher/Permit-class submarine. The Thresher/Permit class was a class of nuclear-powered attack submarines that formed the backbone of the United States Navy's undersea fleet during the Cold War. Originally designated the Thresher class, the name was changed to the Permit class following the loss of the lead boat, USS Thresher (SSN-593). These vessels represented a major technological leap over the preceding Skipjack-class submarine, incorporating advanced sonar, quieter propulsion, and greater operational depth.

Design and development

The design emerged from project SCB 188, driven by lessons from the Skipjack-class submarine and the Regulus missile-carrying Grayback-class submarine. Primary design goals included superior acoustic signature reduction for anti-submarine warfare and integrating the massive BQQ-2 sonar system, which required the distinctive bow-mounted torpedo tubes. The class introduced the S5W reactor plant, a standardized design used in many subsequent U.S. submarines, and HY-80 high-tensile steel for a test depth exceeding 1,300 feet. Key figures in its development included Admiral Hyman G. Rickover of the Naval Reactors branch and designers at Portsmouth Naval Shipyard and General Dynamics Electric Boat. The design phase was heavily influenced by the ongoing technological competition with the Soviet Navy.

Operational history

The first boat, USS Thresher (SSN-593), was commissioned in 1961, with the last, USS Gurnard (SSN-662), entering service in 1968. They served extensively throughout the Cold War, conducting surveillance missions against the Soviet Navy, particularly near Soviet bastions like the Kola Peninsula and the Sea of Okhotsk. Boats such as USS Barb (SSN-596) and USS Pollack (SSN-603) were routinely deployed to the Atlantic Ocean, Mediterranean Sea, and Pacific Ocean. Their missions included tracking Soviet ballistic missile submarines like the Yankee-class submarine and gathering intelligence. Several, including USS Jack (SSN-605), were used to test innovative propulsors. The class remained in frontline service until the 1990s, with the last, USS Tinosa (SSN-606), decommissioning in 1992.

Specifications

The class displaced 3,540 tons surfaced and 3,900 tons submerged, with a length of 279 feet and a beam of 32 feet. Propulsion was provided by one S5W reactor driving two steam turbines and a single shaft, producing about 15,000 shaft horsepower for a submerged speed in excess of 28 knots. Armament consisted of four 21-inch torpedo tubes amidships, firing the Mark 37 torpedo, Mark 14 torpedo, Mark 45 ASTOR nuclear torpedo, and later the Mark 48 torpedo and UGM-84 Harpoon. The primary sensor was the large, bow-mounted BQQ-2 sonar array, supplemented by the BQS-6 active sonar and a towed array on later units. The crew complement was approximately 112 officers and enlisted men.

Variants

The initial Thresher design was followed by three distinct sub-groups. The first four boats (SSN-593-596) had a distinctive stepped sail. The eight "standard" Permit-class boats (SSN-597-603, 612) featured a streamlined sail. The final two boats, USS Jack (SSN-605) and USS Tullibee (SSN-597), were unique variants; *Tullibee* was a smaller, purpose-built hunter with a turbo-electric drive and bow sonar sphere, while *Jack* was a test platform for an experimental counter-rotating propeller system. *Tullibee* is often considered a separate, one-boat class but was built under the same program.

Accidents and incidents

The class is indelibly marked by the loss of USS Thresher (SSN-593) on April 10, 1963, during deep-diving tests east of Cape Cod. The sinking, which claimed 129 lives, was the deadliest submarine disaster in U.S. history. The subsequent investigation by the Court of Inquiry and the SUBSAFE program concluded that a piping failure likely led to flooding and a loss of propulsion. Another significant incident involved USS Guitarro (SSN-665) of the later Sturgeon-class submarine, which sank at its pier at Mare Island Naval Shipyard in 1969 due to a flooding error during construction. The Thresher disaster directly led to the rigorous, ongoing SUBSAFE quality assurance program.

Legacy and significance

The Thresher/Permit class represented the definitive transition to the modern, teardrop-hulled nuclear attack submarine, directly influencing the subsequent Sturgeon-class submarine and Los Angeles-class submarine. The implementation of the SUBSAFE program following the Thresher tragedy remains a cornerstone of United States Navy submarine safety. These submarines were critical in maintaining acoustic superiority over Soviet submarines throughout the 1960s and 1970s. Their design philosophy—emphasizing stealth, advanced sonar, and deep-diving capability—set the standard for all future American attack submarines, culminating in the Seawolf-class submarine and Virginia-class submarine. The wreck of the Thresher, located by the bathyscaphe Trieste II, serves as a solemn memorial and a permanent reminder of the risks of undersea exploration. Category:Submarine classes Category:Cold War submarines of the United States Category:Nuclear-powered attack submarines