USS S-20 (SS-125) was a first-group (S-1 or "Holland") S-class submarine of the United States Navy. Her keel was laid down on 15 August 1918 by the Bethlehem Shipbuilding Corporation in Quincy, Massachusetts. She was launched on 9 June 1920 sponsored by Miss Anne Claggett Zell, and commissioned on 22 November 1922 with Lieutenant John A. Brownell in command.