This single piece of equipment ranks in the top three of most important pieces of equipment on a ship. With out a rudder the ship cannot move where it needs to move and that can cause major problems. The lack of a workable rudder doomed DKM Bismarck. The lack of a working rudder possibly saved USS Enterprise during the Battle of the Eastern Solomons when hers jammed and the Japanese sent a large force to where she should have been.

There has been much research into the history of the rudder. Using a sail to steer a ship is fine as long as you are heading windward. If you need to cut across the wind it becomes harder to do with only your sails. Using rivers current to guide you down stream works well until it is time to dock and there is a strong current pulling you away from your dock.

Steering oars were used by the Phoenicians from 1550 BC. Egyptian tomb painting and even wooden models suggest they used a similar method on the Nile as far back as 3000 BC. Images from ancient Iran and again wooden models suggest boats in this portion of the world used a similar method, a large steering oar off the stern of the boat.
The stern mounted rudder does not appear on ships until the First Century, AD. Almost at the same time Roman and Chinese Naval architects developed the stern mounted rudder as a means of directing a ships course. The use of an oar steering system on large ships died out in medieval times. Larger ships required a better system for steering and a rubber was the only way to go.

Stern mounted rudders were large sections of the ship and were first attached using leather hinges. Chinese ships had rudders that could be raised and lowered as need to prevent them from being damaged. Rudders were so important they were one of the first targets in a battle. As we have seen some ships as late as World War II were fitted with auxiliary rudders. Also during that same war two of the wars iconic ships had damaged rudders help in their eventual fates.

Today large cargo ships are built without rudders. Instead they use a movable pod that houses one of the ships propellers. They use these in combination with bow thrusters to actually move sideways in the water. The cruise ship I was on did this. Watching it dock was so different than watching my destroyer dock.