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Built in 1960, by Ingalls Shipbuilding Incorporated of Pascagoula, Mississippi (hull #135) as the Mobil 8 for the Mobil Oil Corporation of New York, New York.
In 1991, in the wake of the Exxon Valdez incident. In an effort to remove the oil company's physical names from the vessel's names. The Mobil Oil Corporation renamed the tug as the Tatarrax.
In 1991, the tug was acquired by New York Towing Line Incorporated of Hempstead, New York. Where she was renamed as the Nan McKay.
In 1995, she was acquired by the Clearwater Marine Towing Company of Wallingford, Pennsylvania. Where the tug was renamed as the Tenacious.
In 2005, the tug was acquired by the Ryba Marine Construction Company of Cheboygan, Michigan. Where the tug retained her name.
In 2016, she was acquired by Marine Services Incorporated of Oak Park, Michigan. Where the tug retained her name.
Powered by a single, EMD 16-567C diesel engine. She is a single screw tug, rated at 2,000 horsepower.