USS Thresher

1963

Cape Cod, test depth, the implosion Location: Atlantic Ocean, ~220 nmi east of Cape Cod · Coordinates: 41.73°N 65.00°W · Casualties: 129 · Survivors: 0 · Depth: 2,590 m · Cause: implosion — Lost on post-overhaul diving trials off Cape Cod on the morning of 10 April 1963. A probable silver-brazed joint failure in the seawater system at test depth caused flooding, reactor scram, and loss of propulsion. Imploded at approximately 730 metres. · Fate: abyssal · located 1963 · protected · Type: submarine · nuclear attack · Permit class · Tonnage: 3,540 tons · Crew: 129 · Flag: United States · Launched: 1960 American Permit-class nuclear attack submarine, the lead ship of a revolutionary class. On post-overhaul trials off Cape Cod on the morning of 10 April 1963, a probable silver-brazed seawater-joint failure at test depth led to flooding, reactor scram, and loss of propulsion. 129 dead, the worst American submarine loss ever. The investigation produced the SUBSAFE quality-control program, which has overseen the construction of every U.S. Navy submarine since. The Vessel USS Thresher (SSN-593) was the lead ship of the Permit-class nuclear attack submarines of the United States Navy, the design that represented the second generation of American nuclear attack boats after the Skipjack class. She was laid down at the Portsmouth Naval Shipyard in New Hampshire on 28 May 1958 and commissioned on 3 August 1961 as the first production submarine of an entirely new design philosophy: a single sound-quieted hull around a more powerful reactor, deeper test depth, better sonar, and the new Mark 37 homing torpedo. Her design test depth was 400 metres, a depth that placed her operating envelope below any previous American submarine. Her hull was built of HY-80 high-tensile steel, a new alloy that allowed thinner plating at the required pressure. Her reactor was the S5W pressurised water unit, a development of the Nautilus's original S2W; her Mk 113 torpedo fire control system was the first fully digital fire-control system ever installed in a submarine. She was, at commissioning, the most technologically advanced submarine in the world. She was also a prototype. Many of her systems had never been tested at sea in production form. Her first year of service produced a long punch-list of minor and major failures, including the saltwater piping system, the main seawater pump bearings, the atmosphere control system, and the sonar dome. In May 1962 she was withdrawn from the fleet for a 10-month availability at Portsmouth Naval Shipyard to address some 900 work The Disaster The implosion of a submarine at depth is functionally instantaneous. At 730 metres the seawater pressure is roughly 74 atmospheres; the collapse of a submarine hull under such pressure is complete in approximately 100 milliseconds. The crew, including the 17 civilian observers, died without any meaningful interval of awareness. The Navy's investigation identified the proximate cause as the failure of a silver-brazed joint in the saltwater piping system at or near test depth. Salt water entered an engine-room space, shorted an electrical panel, and initiated an emergency reactor scram. The reactor scram removed main propulsion. The emergency main ballast blow failed to complete because moisture had clogged the air-drying strainers of the emergency blow system. Thresher sank from test depth to implosion without the means to arrest her descent. The subsequent Naval Court of Inquiry and the follow-on DSRV submarine-rescue programme produced the most consequential reform in American submarine construction history. The SUBSAFE programme, established 20 December 1963 by direction of the Chief of Naval Operations, mandated extensive redesign of every component of every American submarine whose failure could result in flooding at depth. Silver-brazed joints of the type that had failed on Thresher were to be replaced by welded joints throughout the fleet. Every new American submarine since 1963 has been certified under SUBSAFE. The United States Navy has lost no submarine to a SUBSAFE-