Polar-class icebreakers , are heavy icebreakers operated by the United States Coast Guard (USCG). 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. The vessels conduct Arctic and Antarctic research and are the primary icebreakers that clear the channel into McMurdo Station for supply ships. All are homeported out of Seattle, Washington.