“The second USS Thresher (SSN-593) was the lead boat of her class of nuclear-powered attack submarines in the United States Navy.She was the U.S. Navy’s second submarine to be named after the thresher shark.On 10 April 1963, Thresher sank during deep-diving tests about 350 km east of Boston, Massachusetts,killing all 129 crew and shipyard personnel aboard.Her loss was a watershed for the U.S. Navy, leading to the implementation of a rigorous submarine safety program known as SUBSAFE.The first nuclear submarine lost at sea, Thresher was also the first of only two submarines that killed more than 100 people aboardthe other was the Russian Kursk, which sank with 118 aboard in 2000.