Shannon explained that a leak in the engine room’s seawater system is believed to have caused the tragedy. The leak allowed saltwater in, which shorted-out an electrical panel, causing a loss of power that led to a shutdown of the ship’s nuclear reactor that powered the ship. The failure prevented the Thresher’s ballast tanks from successfully blowing, which would have forced the sub to surface. Instead, the ship imploded as it sank to the ocean’s floor, 8,400 feet down.
The loss of the Thresher was a “watershed event” for the Navy, Shannon told the crowd. It led to the creation of its “Subsafe” program, a stringent quality assurance building standard meant to ensure there would never be another such tragedy. So far, he added, there has never been a submarine lost that was built to Subsafe specifications.
“Believe me, the history of the Thresher was not lost on any of us,” Shannon said. “The sacrifice those men made was impressed upon all of us by our officers and senior members of our crews.”
And yesterday, the evidence of that stood all around, as dozens of submarine veterans from Sub Bases Marblehead and Boston, as well as from New Hampshire’s veterans’ Sub Base Thresher, stood at attention, saluting the heroes lost 50 years ago, as the American flag flew at half-staff behind them.