Recently, the navies of many countries around the world as well as the U.S. and the U.K. have made efforts to apply hybrid electric propulsion system and Integrated electric propulsion system as energy-saving system to naval ships in order to reduce the life cycle cost of ships in line with the reduction of defense budgets and continued high oil prices. In particular, the U.S. and European navies are studying ways to reduce the cost of ship fuel by applying Bidirectional power conversion technology to naval ships equipped with hybrid electric propulsion system. There are no domestic and foreign cases of Bidirectional power conversion technology being applied in combat ships. However, the U.K. and Norway Logistic support vessels as combat support ships, which are highly installed with commercial equipment, are equipped with a hybrid electric propulsion system with Bidirectional power conversion technology to save fuel. Hybrid electric propulsion system has been applied to naval ships, such as Frigate and Logistic support vessel in Korea, but Bidirectional power conversion is not applied and is used only as a motor at low speeds. Therefore, it is necessary to study the energy savings effect of the application of Bidirectional power conversion on hybrid electric propulsion system in order to apply Bidirectional power conversion to domestic naval ships in the future. In this study, the effects of Bidirectional power conversion on the hybrid electric propulsion system for Aegis destroyer, Frigate and Logistic support vessel, which are the representative naval ships applied with the hybrid electric propulsion system, were analyzed. The annual fuel saving effect and the maintenance cost reduction effect were analyzed for each naval ship by considering the operational profile of the ship, the annual operating time of the ship, and the concept of operation of the generator. Although the effects vary slightly depending on the type of the propulsion system, the ship operation profile, and the operation concept of the generator, it has been confirmed that the effect of saving fuel and reducing maintenance cost is very high when applying the Bidirectional power conversion on the hybrid electric propulsion system.