The Polar Star, one of the nation's two heavy-duty icebreakers, is almost ready for service again. The Coast Guard ship is based in Seattle.

WASHINGTON — One of the nation’s two heavy-duty icebreakers is almost ready for service again.

The U.S. Coast Guard reactivated the Polar Star Friday after a four-year, $57 million overhaul at Vigor Industrial shipyard. The 34-year-old ship is to undergo testing next year before once again plying the frozen Arctic regions.

The Polar Star will join the smaller Healy as the Coast Guard’s only two active icebreakers.

A third icebreaker, the Polar Star’s twin, the Polar Sea, was on the verge of being decommissioned and used for spare parts for its sister ship. But an amendment inserted into the Coast Guard reauthorization bill earlier this year by U.S. Sen. Maria Cantwell would block that move until the Coast Guard shows that scrapping the ship is cost effective and develops a plan for additional icebreakers.

The bill — which passed the Senate this week and awaits President Obama’s signature — also would require all three icebreakers to be homeported in Seattle until 2022. That provision was written to prevent a repeat of a previous congressional tussle to relocate the ships to Alaska.

The Polar Star can bust through a two-story wall of ice by backing up and ramming. But the ship is past its original life span. Cantwell and others have argued for beefing up the nation’s ice-breaking capabilities as climate change opens up more previously frozen regions to scientific and commercial exploration.

With the Healy, the only icebreaker presently in active service, the United States has been leasing ships from other countries. A fourth American icebreaker, the Palmer, is privately owned.

The new Coast Guard bill also includes a provision authored by Cantwell giving the National Oceanic and Atmospheric Administration 30 days to declare whether the 2011 Japanese tsunami was a “severe marine-debris incident” and to coordinate a cleanup plan with local officials.

Kyung Song: 202-383-6108 or ksong@seattletimes.com