The USCG Polar class of heavy icebreakers consists of three vessels, the USCGC Polar Star (WAGB-10), the USCGC Polar Sea (WAGB-11), and the USCGC Healy (WAGB-20). The Healy may be considered to be in its own sub-class, as it was built to a modified design and constructed more than a decade after its sister ships. 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.