CONCORD, N.H. — New Hampshire Gov. Maggie Hassan has directed flags to fly at half-staff in recognition of the 50th anniversary of the loss of the USS Thresher submarine.

The 278-foot-long submarine sank in 8,500 feet of water 220 miles off Cape Cod, where it remains.

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The USS Thresher, built at Portsmouth Naval Shipyard and based in Connecticut, was out for a routine deep-diving test when it ran into trouble on April 10, 1963.

A total of 129 Navy crew members and civilian technicians lost their lives in the deadliest submarine disaster in U.S. history.