Book excerpt: Naval Mechanical Engineering: Gas Turbine Propulsion, Auxiliary, and Engineering Support Systems is a technical publication for professional engineers to assist in understanding various ships auxiliary systems. You will learn how they are applied to the overall propulsion plant and how the pumps and valves are used in the systems. Since the auxiliary systems vary between ship types, you will learn the systems in general terms. The maintenance and upkeep of the auxiliary systems are extremely important since, without them, the main engines would not be able to operate. You will be presented with some of the various factors that affect gas turbine performance, procedures for engine changeout, and power train inspection. In conclusion, you will learn a few of the maintenance, operating problems, and repair of pneumatic systems, low-pressure air compressors (LPAC), hydraulic systems, pumps, valves, heat exchangers, and purifiers. Proper maintenance or repair work consists of problem diagnosis, disassembly, measurements, corrections of problems, and reassembly. Use of proper tools, knowledge of the construction of equipment, proper work site management, and cleanliness are keys to successful maintenance and repair work.