KITTERY, Maine — A memorial service marking the 46th anniversary of the sinking of the nuclear submarine USS Thresher drew about 150 family members, friends and veterans to Traip Academy in Kittery.

The ceremony is an annual remembrance of the 129 crew members and civilians who perished when the Thresher went down on April 10, 1963, during sea trials from Portsmouth Naval Shipyard.

The submarine ran into trouble and sank to the bottom of the Atlantic, crushed by the enormous pressure. The accident helped trigger a submarine safety program to correct design and construction problems.

The Portsmouth Herald reported that Capt. Robert Mazzone, commander of the Portsmouth Naval Shipyard and the keynote speaker at Saturday’s event, said the accident continues to sit atop the list of America’s worst tragedies.