Marine Engineering Officers are responsible for the maintenance and operation of the ship's main propulsion machinery, deck machinery, air conditioning plants, refrigeration plants, domestic and electrical services. Depending on the type of ship and operational circumstances, Engineers will be required to keep watches in the ship's Engine Room. The Chief Engineer is in charge of the Engine Department and is responsible to the ship's Master for its efficient operation. Whilst the law demands that only one person should be in overall command of the ship and, by tradition, that person is the Master, the Chief Engineer's status and salary is very similar to that enjoyed by the Master.