The SS Manhattan is an oil tanker that was retrofitted with an ice breaking bow in 1969, and made the first commercial east to west transit of the Northwest Passage. At the time of the passage, the Manhattan was the largest merchant vessel in service, and still holds the title for worlds largest icebreaker and largest commercial American vessel. The vessel was converted to this role after oil had been discovered in Alaska's Prudhoe Bay, and served as a tool to determine the feasibility of transporting oil via ship or pipeline. When the vessel was employed to make the voyage again in the winter and was unable it was determined that the pipeline was a more viable option.
Originally, the SS Manhattan was 931 ft. long and 132 ft. wide with a 52 ft. draft. Multiple yards (to reduce timeframes) were contracted to modify the Manhattan. A 135 ft. new bow, with sections by Maine's Bath Iron Works, was fitted for icebreaking work at Sun Shipbuilding and Dry Dock Company (replacing the forward 65 foot section). Newport News Ship and Alabama Dry Dock both converted sections of the vessel. High-capacity ballast pumps and transverse tanks were fitted, allowing it to rock when stuck in ice. 1.5" steel plate was added to form the ice belt. The vessels large steam-powerplant drives two shafts, each fitted with a five-blade propeller and followed by an individual rudder.
The Northwest Passage transit of the SS Manhattan caused quite a stir in the political arena between Canada and the United States over the sovereignty of the waters of the Northwest Passage, a struggle that is still ongoing as climate change is making the passage more viable.