This academic work discusses the combined gas and steam turbine propulsion systems. Recently, gas and steam turbine propusion systems are becoming increasingly present in the world. The research and development of these systems has lead the improvement in terms of efficiency which is the reason for more frequent use in the ship propulsion system. According to that, in the first part of the work, the schemes of the combined gas and steam turbine propulsion system are provided. Also, the diagrams are provided, which indicate the temperature and exhaust gases from the gas turbine. The first part of the work also presents a thermodynamic efficiency ratio of the combined cycles. The introduction of the second part of this work first discusses the combined gas and steam turbine electric systems (COGES) while in the continuation it explains the fuel characteristics used in gas turbines. Also, the 'washing' and storage schemes of the fuel before the injection are presented. The final part of this work is focused on the main components of the gas and steam turbine propulsion systems. Also, the use of the systems is described in the context of round voyages on tanker and liquefied natural gas tanker ships.