Machinist's mates operate and maintain steam turbines and reduction gears used for ship propulsion and auxiliary machinery such as turbogenerators, pumps and oil purifiers. They also maintain auxiliary machinery outside of main machinery spaces, such as electrohydraulic steering engines and elevators, refrigeration plants, air conditioning systems and desalinization plants. They may also operate and maintain compressed gas producing plants.

EM's are responsible for the operation of a ship's electrical power generation systems, lighting systems, electrical equipment and electrical appliances. The duties include installation, operation, adjustment, routine maintenance, inspection, test and repair of electrical equipment. EM's also perform maintenance and repair of related electronic equipment.

Enginemen (EN) operate, maintain, and repair (organizational and intermediate level) internalcombustion engines, main propulsion machinery, refrigeration, air conditioning, gas turbine engines, and assigned auxiliary equipment on Navy ships; stand safety watches on auxiliary boilers and other assigned equipment.