Ship engineers are responsible for propulsion and other ship systems such as: electrical power generation plant; steam boilers; lighting; fuel oil; lubrication; water distillation and separation; air conditioning; refrigeration; sewage treatment and water systems on board the vessel.
They require knowledge and hands-on experience with electric power, electronics, pneumatics, hydraulics, chemistry, steam generation, gas turbines and even nuclear technology on certain military and civilian vessels.
The two highest ranking subordinates are usually the Main Propulsion Assistant (MPA), responsible for operation and maintenance of propulsion machinery, and the Damage Control Assistant (DCA), responsible for prevention and control of damage.
A DCA often stands routine deck or engineering watches, but spends his off-watch time overseeing maintenance of watertight integrity and firefighting equipment.
A DCA's battle station normally includes responsibility for controlling the ship's stability, list and trim by flooding and dewatering undamaged compartments as necessary to prevent capsizing.