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 (220 mi) east of Cape Cod, Massachusetts, killing all 129 crew and shipyard personnel aboard. It is the second-deadliest submarine incident on record, after the 1942 loss of the French submarine Surcouf, in which 130 crew died. 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.