But it was the Chinese under the Han Dynasty that added a crucial technological development that advanced ship design. During the 1st century AD, they invented the wooden rudder which was used for steering. A rudder is basically a flat sheet of wood, used for steering that is connected to a boat via a hinge (or pivot). Cables connect to the rudder pushing or pulling it to the left or right, thereby turning the ship. The stern-mounted rudder replaced the oar steering system as it required less manpower and didn't interfere with the operation of sails