The USS Thresher (named after the thresher shark) was built at the Portsmouth Naval Shipyard in Kittery, Maine and commissioned in August 1961. It was the lead ship of a class of nuclear-powered attack submarines, “silent guardians” created to find and destroy Soviet submarines. It had a top speed of over 20 knots and a maximum operational depth greater than 400 feet, and it displaced 4,300 tons of water when submerged.
On the morning of April 10, 1963, Thresher departed from Portsmouth to perform deep-diving tests, accompanied by the submarine rescue ship USS Skylark. Fifteen minutes after reaching its test depth, it communicated via underwater telephone that it was experiencing difficulties. Amid garbled transmissions, the Skylark crew reported hearing a sudden noise — “like air rushing into an air tank” — and then, silence. Repeated efforts to reestablish contact failed, and a rescue ship began to recover debris. After a fifteen-ship search operation, on April 11 the Navy declared the Thresher lost at sea. A Naval Court of Inquiry later determined that the accident was likely caused by the failure of a salt-water piping system joint, which in turn led to flooding in the engine room.
The loss of Thresher was the genesis of the SUBSAFE Submarine Safety program, established in June 1963. Affirming the Navy’s commitment to a culture of safety, the program requires annual training of personnel, non-negotiable certification requirements and internal and external audits. The program has been successful: no SUBSAFE-certified submarine has ever been lost. As its inscription states, the commemorative monument honors “the 129 men lost aboard USS Thresher (SSN-593) and their SUBSAFE legacy.”