PORTSMOUTH, N.H. -- Family and friends who lost loved ones when the USS Thresher sank 50 years ago joined in tossing wreaths into the water Saturday in an emotional service in remembrance of the 129 Navy crew members and civilian technicians who lost their lives in the deadliest submarine disaster in U.S. history.

Hundreds gathered for the memorial service at Portsmouth High School that concluded with a small group tossing three wreaths into the Piscataqua River. During the service, a bell tolled 129 times.

The event, along with the dedication of a flagpole Sunday in Kittery, Maine, aims to call attention to the tragedy 220 miles off Cape Cod, which became the impetus for submarine safety improvements.

Vice Adm. Michael Connor, commander of the Navy's submarine forces, acknowledged Saturday that the safety upgrades came at a steep cost to Thresher families.

"I've talked a lot about the good that comes from the Thresher and the Thresher's loss, but that's probably not a consolation to the families who've lost a father or a son," Connor told a packed high school auditorium.

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.

The Navy believes the failure of a brazed weld allowed sea water to spray onto an electrical panel, causing an emergency shutdown of the sub's nuclear reactor. The ballast system also failed, preventing the sub from surfacing.

Filling with water, Thresher descended deeper and disintegrated under the crushing force of the ocean. Its remnants rest on the ocean floor at a depth of 8,500 feet.

Don Wise Jr., 59, of Plaistow, N.H., who lost his dad, said the Thresher crew members were doing something special, serving on what was a technological marvel, the Navy's fastest and deepest-diving nuclear submarine.

"They were going deeper and faster than anyone. I always considered my dad a hero and an adventurer," Wise said Saturday. "These memorials are how I connect my children and grandchildren with my dad."

Former Thresher crew member Frank DeStefano, 79, of Orange Park, Fla., said he owed his life to a three-day assignment to Washington that took him away from the submarine during the fateful sea trials.

He said he's happy to see that annual memorial events provide an outlet for families and friends to grieve.

"The only good part about these memorials is that we can help those who were really affected, like the families," DeStefano said. "And it's great to see the children that have come along."

Lynne Lawrence, of Alexandria, Va., whose father, Richard DesJardins, was one of the civilian technicians who died, attended the service with two siblings.

In a recent interview, she described her father as a fun-loving, busy engineer, and said she was sad he didn't get to see his children become adults or meet his grandchildren.

"It's a profound loss that affects you forever, but you grow from it and move on," she said. "Because you don't really have any other choice."

After the ceremony, a rifle team fired shots as the wreaths - one each for Navy personnel and civilian technicians who died, and one for previous Thresher crew members - were tossed into the river.

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