USCG Polar-capable heavy icebreakers consist of three vessels, USCGC Polar Star, USCGC Polar Sea, and USCGC Healy. Polar Star and Polar Sea comprise the Polar class, while Healy is a larger, more modern design and constitutes an entirely different polar-capable icebreaker class. These cutters, specifically designed for open-water icebreaking, have reinforced hulls, special icebreaking bows, and a system that allows rapid shifting of ballast to increase the effectiveness of their icebreaking. These vessels conduct Arctic and Antarctic research and are the primary icebreakers which clear the channel into McMurdo Station for supply ships. All are homeported out of Seattle, Washington.