KITTERY, Maine — Workers from Portsmouth Naval Shipyard returned to the USS Miami to begin cleaning up Tuesday after a five-alarm fire damaged the forward compartments of the submarine last week.

The U.S. Navy expects it will take three weeks for investigators to determine what started the fire, which began the evening of May 23 aboard the Los Angeles-Class attack submarine.

Firefighters from four states responded to aid the ship’s crew and local firefighters stationed at the shipyard extinguish the blaze about 10 hours later – in the early morning hours of May 24 – according to a release from the shipyard.

“The first phase of clean-up has begun,” according to the press release.

U.S. Sens. Jeanne Shaheen, D-NH, and Susan Collins, R-Maine, who visited the shipyard Friday, said while the Navy will not decide whether the Miami will be repaired until the investigation is complete, the process is well within the capacity of the shipyard’s workforce.

There is no indication the USS Miami, which had been undergoing an Engineered Overhaul (EOH) and is located at Dry Dock 2 at the shipyard since March 1, will be relocated, according to the release.

“Portsmouth Naval Shipyard remains a vital element of the Navy’s submarine maintenance industrial base. The men and women of Portsmouth Naval Shipyard, a field activity of Naval Sea Systems Command, are committed to maximizing the material readiness of the fleet by delivering on-time, affordable quality, safely achieved,” results, according to the release.

No further information was available, according to shipyard spokesman Gary Hildreth.