USS SC-21

USS SC-21, until July 1920 known as USS Submarine Chaser No. 21 or USS S.C. 21, was an SC-1-class submarine chaser built for the United States Navy during World War I.

SC-21 was a wooden-hulled 110-foot (34 m) submarine chaser built at the New York Navy Yard at Brooklyn, New York. She was commissioned on either 20 September or 19 October 1917 as USS Submarine Chaser No. 21, abbreviated at the time as USS S.C. 21.

Assigned to the Second Naval District, S.C. 21 operated with the Experimental Unit at New London, Connecticut.

When the U.S. Navy adopted its modern hull number system on 17 July 1920, Submarine Chaser No. 21 was classified as SC-21 and her name was shortened to USS SC-21.

On 24 June 1921, the Navy sold SC-21 to Joseph G. Hitner of Philadelphia, Pennsylvania.