The USS S-31 was a United States Navy submarine, part of the S-class fleet, launched on March 1, 1923. It was designed for coastal defense and had a displacement of about 1,000 tons when submerged. The submarine was equipped with torpedoes and had a crew of around 40 men, allowing it to operate effectively in shallow waters. During its service, the USS S-31 conducted various training exercises and patrols, primarily in the Pacific Ocean. It was decommissioned in 1931 and later sold for scrap in 1945. The S-class submarines, including the S-31, played a crucial role in the development of submarine warfare tactics during their time.