The USS S-40 was a United States Navy submarine, part of the S-class fleet. Launched on March 1, 1926, it was designed for coastal defense and reconnaissance missions. The submarine was 219 feet long and had a surface displacement of around 1,000 tons. During its service, the USS S-40 operated primarily in the Pacific Ocean. It was decommissioned in 1945 and later sold for scrap in 1946. The submarine played a role in the evolution of naval warfare, contributing to the development of submarine technology during its operational years.