USS D-2 (SS-18) was a D-class submarine of the United States Navy. Her keel was laid down by Fore River Shipbuilding Company in Quincy, Massachusetts, under a subcontract from Electric Boat Company of Groton, Connecticut, as Grayling, making her the first ship of the U.S. Navy to be named for the Arctic grayling, a fresh-water game fish closely related to the trout. Grayling was launched on 16 June 1909, sponsored by Miss C. H. Bowles, and commissioned on 23 November 1909. She was renamed D-2 on 17 November 1911.