This training circular (TC) provides information on the principles of operation and maintenance of marine diesel engines, auxiliary equipment, and related systems. General instructions and precautions requiring special attention are included for guidance for those responsible for training personnel. No attempt has been made to cover all unit models. Specific technical manuals, lubrication orders, or manufacturer's instructions issued with equipment will fully cover required operational and maintenance procedures. This TC is designed for all Soldiers in the marine engineering field. It also provides information for military occupational specialties (MOSs) 88L and 881A. This TC reinforces good marine engineman practices. A good knowledge of marine electricity helps maintain the health and welfare of the crew by promoting the safe operation of the many electrical systems onboard a vessel.