The Boston Navy Yard, originally called the Charlestown Navy Yard and later Boston Naval Shipyard, was one of the oldest shipbuilding facilities in the United States Navy. Established in 1801, it was officially closed as an active naval installation on July 1, 1974, and the 30-acre (120,000 m2) property was transferred to the National Park Service to be part of Boston National Historical Park. Enough of the yard remains in operation to support the USS Constitution. The USS Cassin Young, a World War II-era destroyer serving as a museum ship, is also berthed here, and there is also a dock which serves as a stop on the MBTA Boat. Among people in the area and the National Park Service, it is still known as the Charlestown Navy Yard.