The USS Thresher is an American naval submarine which was lost in 1963 during deep diving exercises. The fate of the USS Thresher triggered a number of concerns about the safety of nuclear-powered submarines, and spurred the United States Navy to establish a safety program to provide enhanced training and disaster response. This program, known as SUBSAFE, provides quality control and safety assurances for the entire nuclear-powered fleet.
This submarine was the lead ship in its class, meaning that it was the first to be built to a new set of specifications. The hull number of the USS Thresher was 593, and technically submarines built after the USS Thresher should be known as Thresher or 593 class submarines, but instead they are referred to as Permit or 594 class subs, after the second ship in the class, due to superstitions about referring to ships which have been lost at sea. The Permit class has been replaced by subsequent new models of nuclear submarine.
Officially commissioned in 1961, the USS Thresher was taken through extensive sea trials by its captain and crew. The submarine experienced several small problems during its period of sea trials, including issues with the ballast tanks and nuclear reactor. With the sea trials finally completed, the USS Thresher was taken out to sea off the coast of Massachusetts for deep sea diving training, accompanied by the USS Skylark, a submarine rescue ship, on 9 April 1963.
The USS Thresher submerged to the expected depth, and then reported that it was experiencing problems and attempting to surface. The report was garbled, and the submarine was never heard from again. The USS Skylark reported the ship lost, and an effort was launched to identify the wreckage and determine whether or not the reactor had leaked. The USS Thresher sank in waters deep enough to cause the ship to implode with pressure, killing the 129 seaman aboard in less than two seconds and scattering the ship across the ocean floor in six pieces. Routine radiological surveys failed to turn up signs that the ship's nuclear fuel had contaminated the area.
Research on the fate of the USS Thresher would seem to suggest that the ship sank because of a failure in its saltwater piping system which ultimately led to flooding of the submarine, turning off the nuclear reactor. Before the sub's crew could power the reactor back up, the ship sank. Recovery of the USS Thresher wreck has not been possible due to the depths at which the sub sank and concerns about nuclear contamination, with several memorials to the ship and her crew being located at various sites in the United States, including Arlington National Cemetery.