Hampton Roads, roadstead, 4 mi (6.4 km) long and 40 ft (12.2 m) deep, SE Va., through which the waters of the James, Nansemond, and Elizabeth rivers pass into Chesapeake Bay. One of the finest natural harbors in the world, it has been a major anchorage point since colonial times and has extensive harbor facilities and shipyards; Newport News and Hampton are on the north shore and Norfolk and Portsmouth on the south. The Port of Hampton Roads, established in 1926 under the State Port Authority of Virginia, is one of the busiest U.S. seaports. Hampton Roads has long been important to the U.S. navy; Norfolk is headquarters for the Atlantic Fleet. A vehicular tunnel (7,479 ft/2,280 m) under the roads opened in 1957. Hampton Roads was the site of the Civil War battle (Mar., 1862) between the ironclads Monitor and Merrimack.