USNS Sioux (T-ATF-171) was a United States Navy Powhatan-class tugboat operated by the Military Sealift Command (MSC).

[4] Her unrefueled range at 13 knots was 10,000 miles (16,000 km)[2] Sioux's aft deck was largely open to accommodate a number of different roles.

[4] The towing system could accommodate either wire rope or synthetic-fiber hawsers and produce as much as 90 short tons of bollard pull.

[9] Sioux accompanied hospital ship USNS Mercy on a 4-and-a-half month training and humanitarian mission to provide health care services to underserved communities in the west Pacific.

[11] Sioux also delivered relief supplies to coastal villages that had been cut-off from aid by road and bridge failures in the wake of a series of typhoons.

[14] In November 1994, Sioux was dispatched to recover the wreck of an F-14 Tomcat which crashed while attempting to land on USS Abraham Lincoln about 50 miles from the coast of souther California.

[15] Sioux was dispatched to assist in the investigation of Alaska Flight 261 which crashed into the Pacific near Anacapa Island in February 2000.

[16] In 2002 Sioux towed the Floating Instrument Platform 20 miles northwest of Oahu to conduct research.

[17] In February 2007, Sioux assisted in the recovery of a MH-60S Seahawk helicopter which crashed on a training mission about 50 miles off the California coast.

[21] In September 2010, Sioux served as a platform for undersea glider tests sponsored by the Office of Naval Research.

[22] In October 2010, Sioux exercised submarine rescue operations with the Chilean Navy in "Chilemar II".

[24] In March 2014, Sioux came to the aid of the Royal Canadian Navy vessel HMCS Protecteur which been disabled by an engine room fire off Hawaii.

[25] Vessels which are retired from Navy service are often towed to various inactive ship maintenance facilities where they are held in reserve.

[20] 2018: On 10 July 2018, Sioux towed ex-Racine out of Pearl Harbor to deep waters where the ship was sunk in a live-fire exercise.

[33] A week later she towed ex-McClusky from Pearl Harbor to an exercise area 55 miles north of Kauai, where this ship was also sunk.

These include:[37] Navy Meritorious Unit Commendation for her work as part of the USNS Mercy task force in 1987.