Kittery, Maine - The first phase of the clean up on the USS Miami has begun.

Workers at the Portsmouth Naval Shipyard were authorized on Tuesday to return to the submarine, which caught fire at 5:41 p.m. on May 23 and burned until 3:30 a.m. the next day.

The investigation into the cause and damage assessment is ongoing, according to a press release today from the shipyard. This process is expected to take about three weeks.

The Miami (SSN 755) was in a dry dock at the shipyard for maintenance and upgrades. The fire damaged the torpedo room, command and control spaces and berthing areas. The reactor had been shut down for more than two months at the time of the fire and the nuclear propulsion spaces were not affected, according to the Navy. No weapons were on board.

Seven firefighters received minor injuries. The submarine's crew and firefighters from the Portsmouth Naval Shipyard Fire Department, the Submarine Base Fire Department in Groton and many local communities extinguished the blaze.

j.mcdermott@theday.com