The U.S. Coast Guard’s only active heavy-duty icebreaker, the 42-year-old Polar Star, returned to its homeport in Seattle today to cap off a challenging months-long mission to Antarctica.

The 13,000-ton cutter is built to break through ice as thick as 21 feet by backing and ramming, and can steam continuously through 6 feet of ice at a speed of 3 knots.

Every year, the Polar Star voyages to the waters off Antarctica to keep shipping lanes open to McMurdo Station, on the southern tip of Ross Island.

The ship left Seattle last November to take part in Operation Deep Freeze 2018, and faced numerous challenges — including two flooding incidents and the loss of one of the ship’s three main gas turbines. No injuries resulted, but the Coast Guard acknowledged that the problems took a toll on the crew and slowed the cutter’s progress to McMurdo.

“Although we had less ice this year than last year, we had several engineering challenges to overcome to get to the point where we could position ourselves to moor in McMurdo,” the ship’s commanding officer, Capt. Michael Davanzo, said in a Coast Guard blog posting.

HAPPENING LIVE: Coast Guard Cutter Polar Star crew returning from 107-day-long Antarctica deployment pic.twitter.com/K5IK48vcM5 — USCGPacificNorthwest (@USCGPacificNW) March 16, 2018

Vice Adm. Fred Midgette, commander of the U.S. Coast Guard Pacific Area, said he was impressed by the crew’s perseverance.

“The crew members aboard Polar Star not only accomplished their mission, but they did so despite extreme weather and numerous engineering challenges,” he said. “This is a testament to their dedication and devotion to duty.”

The Polar Star is scheduled to go into drydock in preparation for its next Antarctic tour of duty, in support of Operation Deep Freeze 2019.

Some lawmakers, including Sen. Maria Cantwell, D-Wash., have expressed concern about the state of the nation’s aging icebreaker fleet. Last year, the Coast Guard determined that the 40-year-old Polar Sea, America’s only other heavy-duty icebreaker, was good only for spare parts. It’s currently sitting inactive in Seattle.

The Coast Guard is moving ahead with plans to build a next-generation heavy icebreaker. The cost has been estimated at $1 billion, with launch scheduled for 2023 — just about the time the Polar Star is expected to reach the end of its extended service life.