KITTERY, Maine -- For Lori Arsenault, who was just eight years old when her father, Tilmon Arsenault, died as the USS Thresher sank in 1963, there's a responsibility to keep the submarine's story alive and to honor the lives of her father and his 128 crew members.

Forty-eight years ago today, April 10, Thresher, a nuclear-powered attack submarine built at Portsmouth Naval Shipyard and commissioned in 1961, was lost about 100 miles east of Cape Cod while conducting sea trials. On board were 16 officers, 96 enlisted men and 17 civilian technicians. The tragedy was remembered Saturday as family and friends of the crew, officers and others gathered at the shipyard, where bells were tolled for all 129 men and a wreath was laid at the water's edge.

"It's a responsibility for us, an obligation for us, to honor their memories because the lessons learned are being put to good use, but we risk forgetting why we're doing them and then they lose their meaning," said Arsenault, of Gorham, who performed the national anthem and Navy Hymn alongside her sister, Debra (Arsenault) Henderson, at the ceremony. "It's important that as long as I live I help them remember, help all of us remember."

Following Thresher's loss, a massive program was undertaken to correct design and construction problems on the Navy's existing nuclear submarines, those under construction and in planning. The Submarine Safety Program was established to assure implementation of technical and administrative requirements to assure seawater is kept out of the submarine and that the sub and crew can recover if there is a seawater casualty.

"There's not a day that passes that we don't work a little harder, just a little smarter, to ensure our work is of the highest quality to keep them safe," said Capt. L. Bryant Fuller, commander of the shipyard, of those who serve in the submarine force. "It's a hallmark of excellence, an admiration of the fleet and a testament to those who gave their lives."

Carol Norton's father, Fred Philip Abrams, returned from 38 months of service in the U.S. Army to take a position at the shipyard, moving up the ranks to civilian inspector when he worked on Thresher. Norton, born and raised in Kittery, said her father went on many sea trials and always came home. But she remembers playing outside after school April 10, 1963, with her brother Jim as their mother walked toward them.

"The look on her face told the story. The words she spoke did not seem real, surely this was a dream and we would wake up soon," she said. "With every single day, hope for the 129 men on Thresher faded. We were alone and the most important person in our lives was gone forever. The memories have sustained us."

While families of 26 Thresher crew members attended Saturday, The Thresher Base, U.S. Submarine Veterans, Inc., hopes to reach the families of all 129 crew members to attend the 50th anniversary memorial service in 2013. "There is no better way to perpetuate the memory of those lost than through family members," said Kevin Galeaz, Thresher Base senior vice commander.