Mark Small

The second USS Thresher (SSN-593) was the lead boat of her class of nuclear-powered attack submarines in the United States Navy. On 10 April 1963, Thresher sank during deep-diving tests about 220 miles (350 km) east of Boston, Massachusetts, killing all 129 crew and shipyard

personnel aboard in the deadliest submarine disaster ever. https://en.wikipedia.org/wiki/USS_Thresher_(SSN-593) …

Her loss was a watershed for the U.S. Navy, leading to the implementation of a rigorous submarine safety program known as SUBSAFE The Submarine Safety Program (SUBSAFE), is a quality assurance program of the United States Navy designed to maintain the safety of its submarine

fleet; specifically, to provide maximum reasonable assurance that submarine hulls will stay watertight, and that they can recover from unanticipated flooding. SUBSAFE addresses only flooding; mission assurance is not a concern, simply a side benefit. Other safety programs

and organizations regulate such things as fire safety, weapons systems safety, and nuclear reactor systems safety. From 1915 to 1963, the United States Navy lost 16 submarines to non-combat related causes. Since SUBSAFE began in 1963, only one submarine,

the non-SUBSAFE-certified USS Scorpion (SSN-589), has been lost. https://en.wikipedia.org/wiki/SUBSAFE