Built in 1975, by McDermott Shipyard Incorporated of Morgan City, Louisiana (hull #208) as the Robin XI for the Robin International Towing Company of Harvey, Louisiana.
In 1985, the tug was acquired by Crowley Marine Services Incorporated of San Francisco, California. Where she was renamed as the Sea Ranger.
She was the seventh Sea Robin class tug for Crowley Marine Services. The last four vessels in the class were fitted with raised bows.
In 2006, the tug was acquired by the Dunlap Towing Company of LaConner, Washington. Where she was renamed as the Polar Ranger.
Powered by two, Caterpillar 3606 diesel engines. With Lufkin RHS 2524 reduction gears, at a ratio of 3.97:1. Turning two, four bladed, 112(in) by 68(in) stainless steel, fixed pitch propellers. For a rated 4,900 horsepower.
Her electrical service is provided by two, 75kW Delco generator sets. Driven by two, Detroit Diesel engines. The tug's capacities are 100,000 gallons of fuel oil, 2,052 gallons of lube oil, 1,026 gallons of hydraulic oil, and 4,200 gallons of potable water.
The towing gear consists of an INTERcon, double drum, towing winch. Outfitted with 3,100(ft) of 2.25(in) wire on one drum and 2,250(ft) of 2.25(in) wire on the second drum.