This textbook covers the basic design and operating principles of the propulsion and auxiliary systems of today’s Naval forces. The topics include the main components in the propulsion and auxiliary systems for both conventional and nuclear steam propulsion, gas turbine power plants (for both ship and aircraft applications), and internal combustion engines. The book also discusses the fundamentals of pneumatic and hydraulic fluid power systems, as well as heating, ventilating, air conditioning and refrigeration (HVAC&R) systems and desalination systems. Other important components covered in greater detail include pumps, valves, pressure and temperature instruments, and heat exchangers. This book is intended to provide the new officer with the essential foundation for understanding the specific mechanical systems they encounter in ships, submarines, aircraft, and land vehicles.