USS SC-209, prior to July 1920, known as USS Submarine Chaser No. 209 or USS S.C. 209, was an SC-1-class submarine chaser in commission in the United States Navy during 1918. She was the victim of the deadliest friendly fire incident involving the U.S. Navy during World War I.

The SC-1 class was a large class of submarine chasers built during World War I for the United States Navy. They were ordered in very large numbers in order to combat attacks by German U-boats, with 442 boats built from 1917 to 1919.