Rudder

A rudder is a primary control surface used to steer a ship, boat, submarine or other vehicle moving through a fluid, working by deflecting the flow of water or air to turn the vessel. Ancient civilizations including Egypt, Persia and Rome steered vessels with oversized steering oars mounted at the side of the hull, a method with real limitations on the open ocean. The stern-mounted rudder, hinged to the sternpost in the design still used today, is first depicted on a Chinese pottery ship model from the Han dynasty in the 1st century AD, roughly a thousand years before an equivalent design appeared in the West, and the design was later adopted by medieval Islamic and European shipbuilders.