(Portsmouth, NH) - The Thresher was the world's most advanced hunter/killer submarine and had undergone upgrades and repairs at the Portsmouth Naval Shipyard. She was lost off the New England coast during sea trials with 129 sailors and civilians on-board.

I remember the day well. I was living in Somersworth and one of our neighborhood
friends lost his dad, one of the civilians taking part in the sea trials.
The USS Thresher was located on the ocean floor under 84-hundred feet of water just east of Cape Cod.
55 years later, the exact cause of the Threshers demise has not been completely solved.