USS Thresher
USS Thresher was the lead ship of its class, which became known as the Permit class after Thresher was lost at sea in April 1963. It was built to be the quietest and fastest submarine in the world at Portsmouth Naval Shipyard beginning in 1958, and was commissioned into the fleet in 1961. Thresher was designed as a platform for new and emerging technologies in undersea warfare, and spent its all too brief career in the Atlantic and Caribbean Sea, operating with other vessels of the US Navy before returning to Portsmouth for evaluation of the ships systems, upgrades, and repairs. In April 1963 it was again ready for sea for tests.
On April 9, 1963 Thresher, accompanied by the submarine rescue ship Skylark, began its dive trials as part of its post shipyard availability tests. About 200 miles east of Cape Cod Thresher dove, surfaced, and dove again remaining submerged throughout the night. The following morning Thresher contacted Skylark and announced the initiation of deep dive tests, in which the submarine was to submerge in steps to its test depth, leveling off and checking all ship’s systems as the crew worked the vessel down. Skylark received messages which were garbled, though it was understood that the submarine was attempting to blow its ballast tanks with high pressure air.
That message alone was an indication of a serious problem encountered during the dive. One further garbled message was heard, and then nothing more. That evening Navy officials began notifying next-of kin that the submarine was missing and by the following morning it was announced that Thresher, only days after an overhaul, had been lost with all hands, and with several civilian shipyard workers and technical representatives aboard. It was the first loss of a nuclear submarine, and the investigation into what happened, while speculative in many ways, changed the way in which nuclear submarines were built and the crews trained.
The loss of Thresher, in the company of another vessel and with civilian experts onboard as well as a highly trained crew caused the Navy to initiate procedures which ensured redundancy of essential systems, and controls over the way work is accomplished aboard the vessels, both in port and at sea. It was believed that a single brazed weld failed, which led to a sequence of events which caused the loss of the ship, including freezing in the ballast control systems, and lack of the ability to quickly control leaks. The Navy initiated the SUBSAFE program, which addressed the issues of design, training, materials, and inspections. All submarines must be SUBSAFE certified.
Since the inception of SUBSAFE the United States Navy has lost just one submarine, USS Scorpion. Scorpion had not been SUBSAFE certified at the time of its loss, to causes still the subject of debate. When Thresher imploded the event was recorded on underwater sonar, and analysis of the recording revealed that the implosion event was a shock 0.1 seconds in duration, meaning that the 129 men aboard the vessel never felt anything once the ship was at crush depth.