Other Characteristics: The shell plating and associated internal support structure are fabricated from steel that has especially good low-temperature strength.  The part of the hull designed to break ice is 1.75 inches thick in the bow and stern sections.  The hull shape is designed to maximize icebreaking by efficiently combining the forces of the ship’s forward motion, the downward pull of gravity on the bow, and the upward push of the buoyancy of the stern.  The curved bow and heavy weight allow the vessels to force ice edges to break off downward.

History: On February 11, 1981, Polar Sea became the first ship ever to reach Point Barrow, Alaska in the middle of winter.  She is also one of only three ships that has every completely transited the Arctic Ocean and circumnavigated North America.  In 1985, Polar Sea triggered a diplomatic event by navigating the Northwest Passage from Greenland to Alaska without authorization from the Canadian government.  The U.S. argued that the Northwest Passage was an international strait open to shipping and sought only to notify Canada rather than ask for permission.  Canada regarded the move as a breach and disregard of sovereignty.  An agreement was reached two years later that stipulated that the U.S. would ask for permission before navigating the disputed waters.  Polar Sea went out of service in 2010 due to failure of five of her six main diesel engines.  In February 2017, the refurbishment of Polar Sea was denied, leaving her to be used as a “parts donor” for Polar Star.