USCGC Polar Sea (WAGB-11) is a United States Coast Guard heavy icebreaker. Commissioned on 23 February 1977, the ship was built by Lockheed Shipbuilding and Construction Company of Seattle along with her sister ship, Polar Star (WAGB-10). Her home port is Seattle, Washington. Polar Sea has been out of service due to failure of five of her six Alco main diesel engines. Machinery Polar Sea has a computerized propulsion control system to effectively manage six diesel-powered propulsion generators, three diesel-powered ship's service generators, three propulsion gas turbines, and other equipment vital to the operation of the ship. Its three shafts are each turned by either a two diesel-electric or one gas turbine power plants. Each shaft is connected to a 16-foot (4.9-m) diameter, four-bladed, controllable-pitch propeller. For all three shafts, the diesel-electric plants can produce a total of 18,000 shaft horsepower (13,425 kilowatts) and the gas turbine plants a total of 75,000 demand shaft horsepower (56 MW) or 60,000 continuous horsepower (44.8 MW). Hull design and strength Polar Sea has sufficient hull strength to absorb the high-powered icebreaking common to her operations. The shell plating and associated internal support structure are fabricated from steel with superior low-temperature strength. The portion of the hull designed to ram ice is 1 inches thick (44 mm) in the bow and stern sections, and 1 inches thick (32 mm) amidships. The hull strength is produced almost entirely from a sophisticated internal support structure that features canted ribs for approximately the forward two-thirds of the ship's frame. Polar Sea'''s 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 inherent buoyancy of the stern. The curved bow and heavy weight allows Polar Sea to force ice edges to break off downward as cusps. This design does not use sharp edges or hammer-like blows to cut or break the ice, as the round bow and massive weight are sufficient. With high power to back it up, the 13,000-ton (13,200-metric ton) Polar Sea is able to continuously progress through 6 feet (1.8 m) of new hard ice at 3 knots (6 km/h) and break up to 21 feet when using back-and-ram methods. An extreme exception to this occurred during a rapid transit to Pt. Barrow, Alaska between January 29 and February 11, 1981. While traversing 1000