Posted by: arbeam | March 20, 2013

Fifty years ago: USS Thresher (SSN-593) Lost

USS Thresher (SSN-593)

USS Thresher (SSN-593)

In company with Skylark (ASR-20), Thresher put to sea on 10 April 1963 for deep-diving sea trials off of Portsmouth Naval Shipyard. In addition to her 16 officers and 96 enlisted men, the submarine carried 17 civilian technicians to observe her performance during the deep-diving tests.

Fifteen minutes after reaching her assigned test depth, the submarine communicated with Skylark by underwater telephone, apprizing the submarine rescue ship of difficulties. Garbled transmissions indicated that–far below the surface–things were going wrong. Suddenly, listeners in Skylark heard a noise “like air rushing into an air tank”–then, silence.

Efforts to reestablish contact with Thresher failed, and a search group was formed in an attempt to locate the submarine. Rescue ship Recovery (ASR-43) subsequently recovered bits of debris, including gloves and bits of internal insulation. Photographs taken by bathyscaph Trieste proved that the submarine had broken up, taking all hands on board to their deaths in 5,500 of water, some 220 miles east of Boston. Thresher was officially declared lost in April 1963.

Subsequently, a Court of Inquiry was convened and, after studying pictures and other data, opined that the loss of Thresher was in all probability due to a casting, piping, or welding failure that flooded the engine room with water. This water probably caused electrical failures that automatically shutdown the nuclear reactor, causing an initial power loss and the eventual loss of the boat.

Thresher is in six major sections on the ocean floor, with the majority in a single debris field about 400 yards square. The major sections are the sail, sonar dome, bow section, engineering spaces, operations spaces, and the tail section.

Owing to the pressurized-water nuclear reactor in the engine room, deep ocean radiological monitoring operations were conducted in August 1983 and August 1986. The site had been previously monitored in 1965 and 1977 and none of the samples obtained showed any evidence of release of radioactivity from the reactor fuel elements. Fission products were not detected above concentrations typical of worldwide background levels in sediment, water, or marine life samples.

From this tragic event, the Submarine Safety (SUBSAFE) Program was established on December 20, 1963 to ensure implementation of recommendations resulting from findings of the THRESHER Court of Inquiry and THRESHER Design Appraisal Board. Simply stated, the purpose of the SUBSAFE Program is to provide maximum reasonable assurance that seawater is kept out of the submarine and that the submarine and crew can recover if there is a seawater casualty.

Naval History and Heritage Command

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