USCGC Polar Star (WAGB-10) is a United States Coast Guard heavy icebreaker. Commissioned in 1976, the ship was built by Lockheed Shipbuilding and Construction Company of Seattle, Washington along with sister ship, . Homeported in Seattle, Polar Star operates under the control of Coast Guard Pacific Area and coordinates her operations through the Ice Operations Section of the United States Coast Guard. After Polar Sea was deactivated in 2010, Polar Star became the US's only heavy icebreaker. The Coast Guard's only other icebreaker, , despite being classified as a "medium icebreaker", is actually larger than 'Polar Star' (13,623 LT versus 16,000 LT). Replacement ships for what is called the Polar Security Cutter program have been ordered for a new generation of USCG icebreakers. Design In August 1971 the Secretary of Transportation announced awarding of a contract to Lockheed Shipbuilding and Construction Company of Seattle, Washington, "to build the world's most powerful icebreaker for the US Coast Guard," Polar Star, the first of two "Polar-Class" icebreakers. The ship's three shafts are turned by either a diesel-electric or gas turbine prime mover. Each shaft is connected to a diameter, four-bladed, controllable-pitch propeller. The diesel-electric plant can produce , and the gas turbine plant a total of . Polar Star'''s shell plating and associated internal support structure are fabricated from steel that has especially good low-temperature strength. The portion of the hull designed to break ice is thick in the bow and stern sections, and thick amidships. The curved bow allows Polar Star to ride up on the ice, using the ship's weight to break the ice. The 13,000-ton (13,200-metric ton) Polar Star is able to break through ice up to thick by backing and ramming, and can steam continuously through of ice at . Later upgrades allowed it to serve as a scientific research platform with five laboratories, additional space for seven portable laboratories on deck and accommodations for up to 35 scientists. Operational history In May and early June 1976 Polar Star conducted ice trials in the Arctic regions during Arctic West Summer (AWS76) operations. The starboard controllable pitch propeller failed, followed up shortly by the same type of failure on the port propeller. Removal of the wing propellers and opening of the hubs revealed massive failures of the links, link bearings, and drive pins. While the centerline propeller functioned satisfactorily, it too displayed evidence of incipient failure of the link