USNS Sioux (T-ATF-171)

USNS Sioux (T-ATF-171) is a United States Navy Powhatan-class fleet ocean tug in service since 1981.

Sioux was laid down on 22 March 1979 by the Marinette Marine Corporation at Marinette, Wisconsin. Launched on 15 November 1980, and delivered to the U.S. Navy on 1 May 1981, Sioux was assigned to the Military Sealift Command (MSC), and placed in non-commissioned service as USNS Sioux (T-ATF-171) in 1981.

Sioux is in active service.