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''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. In addition to the two ''Polar''-class icebreakers, the USCG has a third polar-capable icebreaker, .〔(【引用サイトリンク】title=Northrop Grumman to Supply Polar Ice Breaker Navigation Support for U.S. Coast Guard )〕 Both ''Polar Star'' and ''Polar Sea'' are near the end of their effective lifetimes, and have spent years moored because they were in need of expensive and unbudgeted upgrades.〔 〕〔 〕〔 〕 In November 2013 four Senators proposed an amendment to the 2014 Defense Appropriations Act authorizing the construction of four new Polar class vessels, at a cost of $850 million each.〔 〕〔 〕〔 〕 The four Senators sponsoring the amendment were Maria Cantwell and Patty Murray, from Washington, and Mark Begich and Lisa Murkowski, from Alaska. According to the ''Seattle Times'' the chances that the amendment will survive into the bill, as passed, are slim. ==References== 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Polar-class icebreaker」の詳細全文を読む スポンサード リンク
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