Sioux was built in 1916 by the American Ship Building Company, Cleveland, Ohio, was acquired by the U.S. Navy on 1 December 1917 from the Clyde Steamship Co., New York City, and commissioned the same day as a unit of the Naval Overseas Transportation Service.

After discharging her cargo of coal, she sailed from Glasgow on 12 October, returning to Norfolk on 1 November.

Sailing again from Norfolk on 28 November, this time on a U.S. Army account, she arrived at La Pallice, France, on 16 December.

There, she received urgent voyage repairs and was held in European waters as being unsuitable for North Atlantic use during the winter months.

Selected for demobilization, she sailed on 19 February 1919, via the southern route, and arrived at Norfolk on 21 March.