Once all mechanical components are manufactured, purchased and obtained, they must be installed onboard the ship. Outside machinist apprentices install, repair and test a ship’s major machinery and other mechanical components. Many of these systems are responsible for the ships’ propulsion, steering and weapons systems. They learn the safe operation of shop machines and hand and power tools to install and test systems on nuclear reactors, turbines, generators, pumps, propellers, rudders, elevators, periscopes and armaments. Apprentices also learn the function and operation of motors, pumps and valves.