The USS Thresher (SSN-593) was a nuclear-powered attack submarine commissioned at the Portsmouth Naval Shipyard in Kittery, Maine. As the lead vessel of her class, Thresher was designed to operate at greater depths and speeds than earlier submarines. On April 10, 1963, following an overhaul, Thresher embarked on deep-diving tests approximately 220 miles east of Cape Cod, Massachusetts, accompanied by the submarine rescue ship USS Skylark (ASR-20). During these tests, Skylark received garbled communications from Thresher before all contact was lost. Subsequent searches revealed that Thresher had sunk, resulting in the tragic loss of all 129 officers, crewmen, and civilian technicians aboard. Investigations suggested that a probable cause was a piping failure leading to a loss of power and the inability to blow ballast tanks rapidly enough to prevent sinking.