As melting sea ice opens new sailing routes through Arctic latitudes, the U.S. Coast Guard is accelerating plans to add new icebreakers to its aging fleet.

In September, President Obama moved up plans to buy at least one new Arctic icebreaker from 2022 to 2020. And in January, the Coast Guard took another step toward that goal, announcing it would set acquisition requirements by March for two heavy icebreakers that will cost up to $1 billion each and be capable of operating for up to 40 years.

These herculean vessels must be able to crack through ice up to six feet thick, breaking an 83-foot-wide channel while steaming along at a speed of three knots. Combining endurance with great strength, the ships must also be capable of cruising at 12 knots in open water, with a range of 21,500 nautical miles and 80 days without taking on food or fuel.

Even on the new schedule, the U.S. will be playing catchup to its international rivals. The new additions would bring the U.S. icebreaking fleet up to five vessels, lagging far behind the estimated 40 icebreakers under Russian command.