The USS O-3 was a submarine of the United States Navy, commissioned in 1918. It was part of the O-class submarines, designed for coastal defense and reconnaissance missions. The vessel was 165 feet long and had a surface displacement of around 500 tons. During its service, the USS O-3 conducted various training exercises and operations, primarily in the Atlantic Ocean. It was decommissioned in 1924 and later sold for scrap in 1931. The submarine is notable for being one of the early examples of underwater warfare technology in the U.S. Navy.