USS Thresher (SSN 593)

On 10 April 1963, while engaged in a deep test dive, the nuclear submarine USS THRESHER (SSN 593) was lost at sea with all persons aboard. Based on the findings of a Court of Inquiry and the subsequent Joint Congressional Committee on Atomic Energy hearings into the loss of the THRESHER, it was concluded that a flooding casualty in the engine room, resulting from a piping failure in one of the salt water systems, was the most probable cause for the loss.

A THRESHER Design Appraisal Board determined that, although the basic design of this submarine class was sound, measures should be taken to improve the level of confidence in the material condition of the hull integrity boundary and in the ability of submarines to control and recover from flooding casualties. Thus the genesis of the Level I/SUBSAFE Program. The program establishes control for procurement, inspection, certification, test, identification, documentation, record control, storage, issue, turn-in, recall and disposal. Level I/SUBSAFE Stock Program materials are intensively managed and controlled. They require certification with traceable objective quality evidence. Items include submarine hull pressure boundary fittings, high pressure air and gas components, high pressure/temperature steam system components and selected safety related equipment on surface ships and submarines.