The United States D-class submarines were a trio of submarines built for the United States Navy in the first decade of the 20th century. All three ships served during World War I providing training for crews and officers on the U.S. East Coast, before the class was decommissioned and sold for scrap in 1922.

The C-class submarines were five United States Navy submarines built by the Fore River Shipbuilding Company in Quincy, Massachusetts, under a subcontract from the Electric Boat Company. Built between 1906 and 1909, and in commission from 1908 to 1919, all five were subsequently sold for scrap in 1920. They were considerably larger than the preceding B-class at 275 tons submerged vs. 173 tons submerged, and were the first United States submarines with two-shaft propulsion, doubling the machinery of the B class.