The lower Thames River has a long naval presence centered on the Naval Submarine Base New London in Groton, first built as a naval yard and storage depot in 1868 and made a naval base in 1915. At the river's entrance, the Electric Boat Division of General Dynamics has been involved in submarine development and construction since the USS Holland was commissioned in 1900. On the New London side, Fort Trumbull protected the harbor during the 18th and 19th centuries, then took on a new role early in the 20th century when submarines proved their worth at the onset of World War I and the Secretary of the Navy established a civilian-military research station there to develop anti-submarine warfare technologies. Submarines carrying these systems served in war zones during both World Wars and the Cold War. The base also trains highly skilled submariners through what is known as Sub School, with qualification as a submariner completed at sea. The Submarine Force Museum preserves the history of the Silent Service and the evolution of submarines that transformed naval warfare, including a full-scale replica of David Bushnell's Turtle, launched in Connecticut in 1776 during the American Revolution, torpedoes, models of all classes of U.S. Navy submarines, and the USS Nautilus, built at Electric Boat in 1954, the world's first nuclear-powered submarine, now permanently moored on the Thames River.