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.

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.