Video: 'USS Thresher (SSN-593) (documentary)'

(Wednesday, April 10, 1963, 9:18 a.m. EST) — The fast-attack nuclear submarine USS Thresher (SSN-593) sank today during deep-diving tests 220 miles east of Cape Cod, Massachusetts, killing the 112 U.S. Navy personnel and 17 civilians on board.

Deep-sea photography, recovered artifacts, and an evaluation of Thresher’s design and operational history permitted a court of inquiry to conclude that the submarine had probably suffered the failure of a salt-water piping system joint that relied heavily on silver brazing instead of welding.

Video: 'The Classified Sinking of the Submarine USS Thresher'

President John F. Kennedy ordered all flags to be flown at half-staff from April 12-15 in honor of the 129 lost submariners and shipyard personnel.

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 third of four submarines lost with more than 100 people aboard, the others being Argonaut, lost with 102 aboard in 1943, Surcouf sinking with 130 personnel in 1942, and Kursk, which sank with 118 aboard in 2000.