This weekend a memorial for the 50th anniversary of the deadliest submarine disaster in U.S. History will occur.

The memorial will occur in Portsmouth, N.H this weekend.

April 10, 1963 the USS Thresher (SSN-593), a fast attack nuclear submarine, and the first of its named Thresher-class (later changed to Permit-class) submarine sank about 220 miles off Cape Cod.

The Navy believes that during sea trials and drills a leak in a pipe caused an electrical panel to short out.

A series of subsequent events where the reactor plant was shut down caused the ship to attempt an emergency blow.

Emergency blow is meant to take compressed air from storage tanks and use it to quickly force water from the ballast tanks, surfacing the submarine.

It is believed that the pipes for the emergency blow system were too small and thermal effects along with moisture in the pipe caused an ice plug in the line that prevented the emergency blow from functioning.

The ship sank past crush depth and imploded under sea pressure.

All 129 sailors and personnel on-board were lost.

Following the disaster many operating procedures and design criteria were changed for safety.