I was on LST 1180 of the Newport Class. On these ships aft steering was manned anytime we were underway.
We had twin rudders also; each turned by a large hydraulic motor. Large pumps drove these motors. The person on watch could switch from bridge control to local control and steer the ship with a small wheel we called a trick wheel that in turn controled the hydrolic system. The bridge would give steering commands to him via sound powered phones.
Hydraulic systems rely on oil under pressure to do the work. Some bubbles in the system may reduce efficiency under load. You can usually tell if you are getting air in the system when the noise level goes up. Too much air and the system will fail. The system uses a lot of valves, switches and controls to make it work. These items are generally the cause of failures. An old salt told me one time there are two things on the face of this earth you can never stop from leaking, steam and hydraulic fluids.
Each rudder had a main hydraulic pump and a backup pump that could be switched in if the main pump failed.
On LST 325 you are correct about the large wheel and cables. In the event of a hydraulic system failure this wheel and cables can be used to manually turn the rudder.
It is a slow process, however, and quick turns can not be made.
On the LST 1180 I was on we had a pair of chain falls as a backup. In the event of a hydraulic failure these were attached to the bulkhead and the other end to the large armature fastened to the rudder. To turn the rudder, one sailor would tighten the falls while the other would slack his. It took some practice to get good at this. Like the LST 325 system, turning was slow.
As a final backup, you notice the LST 325 has twin propellers. These propellers are attached to two independent drive shafts. By controlling the speed and direction of these propellers the ship can still be maneuvered. If you noticed when the LST gets underway in Evansville and turns around, one propeller is pushing forward and the other is going in reverse. This turns the ship in a much smaller radius than the rudders alone could.
On a final note, if a ship has steering problems the captain immediately orders the signalman to hoist up warning pennants or display signal lights to let other ships know she is in trouble. The ship in distress is given a wide berth and other ships maintain a safe distance. Skivywaver can give you more details on that process.
The final backup, which is also used in the event of motor failure, are the ships oars. If you notice along the deck on both sides of the ship there are round fixtures. These are normally used to pass mooring lines and cables through when the ship is docked. While underway if we loose power, we retrieve the long oars from their storage brackets in the tank deck and pass them through these oarlocks. With these the ship can be rowed safely out of harms way.