On this day in history, 1963, the USS Thresher (SSN 593) sank during sea/dive trials. One hundred and twenty-nine officers, enlisted men, and shipyard workers were killed. Twelve of those who perished were US Naval Academy graduates, but one graduate recently having completed nuclear power training and sub school was delayed in reporting aboard Tresher.

The loss of the Thresher was a watershed for the U.S. Navy, leading to the implementation of a rigorous submarine safety program known as SUBSAFE, 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. A “Thresher Design Appraisal Board” determined that, although the basic design of the Thresher class was sound, measures should be taken to improve the condition of the hull and the ability of submarines to control and recover from flooding casualties. The SUBSAFE program became a model for a similar program implemented by NASA following the 2003 loss of Space Shuttle Columbia.

Following Navy tradition, this class of subs was originally named Thresher after the lead boat. When Thresher was struck from the Naval Vessel Register on 10 April 1963, the class name was changed to that of the second boat, Permit. Having been lost at sea, Thresher was not decommissioned by the U.S. Navy and remains on “Eternal Patrol.”