Science & Nature • Naval Disaster

USS Thresher

USS Thresher (SSN-593) was a U.S.

By Ethan Anderson| Reviewed by Olivia Bennett, Standards & Fact-Checking Lead| Updated July 26, 2026|2 min read| Fact-checked

USS Thresher (SSN-593) was a U.S. Navy nuclear-powered attack submarine that sank during deep-diving tests on 10 April 1963. All 129 people aboard died, making it the deadliest submarine disaster in U.S. history. The wreck lies on the Atlantic seabed east of Cape Cod and is treated as a naval war grave.

History

USS Thresher was the first submarine of its class and entered service as a nuclear-powered attack submarine. It was lost during post-overhaul sea trials in April 1963.

Sinking and investigation

The submarine reported difficulties during a dive, then contact was lost. Navy investigations concluded that flooding from a likely piping failure caused loss of power and the inability to surface before the boat reached crush depth.

Wreck location

The wreck was found on the ocean floor about 8,400 feet down, roughly 220 miles east of Cape Cod. The site is regarded as a permanent war grave.

Legacy

The loss of Thresher became the deadliest submarine disaster in U.S. Navy history. It directly influenced submarine safety practices and the creation of the SUBSAFE program.

Key facts

USS Thresher sank during sea trials and deep-diving tests on 10 April 1963.
All 129 people aboard died, including Navy personnel and civilian shipyard technicians.
Naval investigations said the most probable cause was flooding from a piping failure that led to electrical failure and loss of propulsion.
The submarine descended beyond crush depth and imploded under pressure.
The disaster helped drive major U.S. Navy submarine safety reforms, including the SUBSAFE program.

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Canadian context

The disaster is relevant to Canadian readers because it is a major Cold War naval event in the North Atlantic and a landmark case in submarine safety, search-and-recovery history, and maritime disaster investigation.

Frequently asked questions

What happened to USS Thresher?

USS Thresher sank during deep-diving sea trials on 10 April 1963 after losing propulsion and control, then imploded under pressure. All 129 people aboard were killed.

How many died on USS Thresher?

All 129 people aboard died.

When did USS Thresher sink?

USS Thresher sank on 10 April 1963.

Where is the USS Thresher wreck?

The wreck lies on the Atlantic seabed about 220 miles east of Cape Cod, Massachusetts, at roughly 8,400 feet depth.

What caused USS Thresher sinking?

The Navy’s investigation identified a likely piping failure that caused flooding, electrical failure, and loss of propulsion; the submarine then could not recover before reaching crush depth.

USS Thresher vs Scorpion

Thresher sank in 1963 and killed 129 people; USS Scorpion sank in 1968 and killed 99 people. Both were U.S. Navy nuclear submarines lost in the Atlantic, but their causes were different and Thresher led to major safety reforms.

References

U.S. Naval History and Heritage Command — https://www.history.navy.mil/content/history/museums/nmusn/explore/photography/ships-us/ships-usn-t/uss-thresher-ssn-593.html
Supports: Sinking date, fatalities, wreck location, and Navy finding of probable piping failure
U.S. Naval Institute — https://www.usni.org/magazines/naval-history-magazine/2023/april/what-killed-thresher
Supports: Most probable cause involving flooding and piping-system failure
Encyclopaedia Britannica — https://www.britannica.com/topic/Thresher-submarine
Supports: Overview, date of sinking, fatalities, cause, and wreck depth
U.S. Navy — https://www.navy.mil/Press-Office/Press-Releases/display-pressreleases/Article/2358204/department-of-navy-releases-records-related-to-loss-of-uss-thresher/
Supports: Date of sinking, total on board, and note that multiple weaknesses contributed to the loss
U.S. Naval Sea Systems Command — https://www.navsea.navy.mil/Media/News/Article/3354927/uss-thresher-a-loss-a-legacy/
Supports: Uncontrolled flooding, descent below crush depth, and implosion