KITTERY — The town that’s home to the Portsmouth Naval Shipyard dedicated a flagpole in memory of the crew of the USS Thresher on Sunday, a day after an emotional memorial service marking the 50th anniversary of the deadliest submarine disaster in U.S. history.

At a morning ceremony at Memorial Circle in Kittery, hundreds of people gathered around the newly installed flagpole that towers to a height of 129 feet — one foot for each of the 129 men who lost their lives.

The memorial service was held Saturday for the Thresher, which was built at the shipyard and based in Connecticut. The 278-foot-long submarine sank in 8,500 feet of water 220 miles off Cape Cod, where it remains.

“The loss of 129 officers, sailors and civilians continues to fill our hearts with grief,” as well as pride and gratitude, said U.S. Sen. Susan Collins of Maine, one of the speakers at the flagpole dedication. “The USS Thresher Memorial guarantees we will never forget those who are on eternal patrol.”

Marcye Philbrook, a Kittery resident who was 2 when her father, Quartermaster Julius Marullo Jr., died aboard the Thresher, told the Portsmouth Herald there was some disagreement about whether the memorial flagpole was too tall, but for her, the size was just right.

“It meant more than I ever could have imagined when that flag went up,” she said. “I think it’s just perfect.”

Collins and Vice Adm. Michael Connor, commander of the U.S. Navy submarine forces, both pointed out that the tragedy led to the implementation of a program called SUBSAFE, an extensive series of design modifications, training and other improvements to ensure similar disasters didn’t occur.

“Their loss was certainly not in vain,” Connor said. “They made submarines safer, but they also made the world safer.”