A recent trend in designing naval ships is to improve performance through using more electric equipment. The reliability and quality of the onboard electric power, therefore, becomes critical as the ship functionality would entirely depend on its availability. This paper investigates the possibility of using Flywheel Energy Storage Systems (FESS), similar to those earlier developed for commercial applications, to address issues related to onboard power supplies. A design of a FESS for onboard power backup and railroad electrical stations is presented. The FESSs power output parameters are 500kWx30sec in high-duty mode and up to 2MW in pulse mode. High power output is one of the main advantages of FESS over commercially available electrochemical batteries. The other advantages include essentially an unlimited number of charge/discharge cycles, observable state of charge and environmental friendliness. Designs of the main FESS components are discussed: low-loss magnetic bearings, an energy-storage hub, a high-efficiency motor/generator and power electronics.