The U.S. Coast Guard has a heavy ice-breaking ship working in the Arctic region for the first time in more than four years.

The ship is capable of breaking through 21 feet of ice, and is being employed amid cries from environmentalists and politicians that Arctic ice is thinning.

Increased interest in developing the Arctic has spurred demand for ice-breakers to be sent up north.

“Every year we have more Coast Guard assets going up north,” said Coast Guard Chief Warrant Officer Allyson Conroy. “We realized we really needed to have these heavy ice breakers up there and it would be beneficial to retrofit one.”

With two of the U.S.’s three heavy ice-breakers out of commission, the Polar Star was refurbished at an estimated cost of $55 million to help keep Arctic waterways clear of ice and to be used as a science platform.