KITTERY — Investigators have begun their damage assessment and investigation following a fire aboard a billion-dollar nuclear-powered submarine being overhauled at Maine’s Portsmouth Naval Shipyard in a dry dock.

A shipyard spokeswoman says the USS Miami was ventilated to remove smoke Friday and people were allowed into the fire-damaged forward compartments.

U.S. Sens. Susan Collins of Maine and Jeanne Shaheen of New Hampshire say the Navy has dispatched three investigative teams to the Kittery shipyard.

The fire started Wednesday night. It damaged several rooms, including the command and control center, but spared the sub’s nuclear propulsion.

It’s not yet clear whether the sub can be salvaged or what caused the blaze.

The USS Miami cost about $900 million when it was built. The newest attack subs are about $2.6 billion.