Which attack submarine was lost at sea in the Mediterranean Sea during the cold war?

The attack submarine lost at sea in the Mediterranean during the Cold War was the USS Thresher (SSN-593). It sank on April 10, 1963, during deep-diving tests off the coast of Massachusetts, but its loss was initially associated with a broader context of Cold War tensions. The submarine was later officially classified as lost, and all 129 crew members on board were killed. The incident led to significant changes in submarine safety protocols and design improvements.