COGAG COGAG Combined Gas and Gas is a marine propulsion system where two or more gas turbines drive the same shaft. Individually or together. , short for Combined Gas and Gas, refers to a naval propulsion system that uses two (or more) gas turbines connected to a single propeller shaft via a combining gearbox. The turbines can operate individually for fuel efficiency at lower power demands, or together to deliver high thrust and speed. Unlike CODAG CODAG Combined Diesel and Gas is a marine propulsion system that combines diesel engines and gas turbines to drive the same shaft, depending on operational needs. or CODOG CODOG Combined Diesel or Gas is a marine propulsion system where either diesel engines or a gas turbine - never both simultaneously - drive the same propeller shaft. , COGAG systems rely entirely on gas turbines, without any diesel engine involved.
This configuration is chosen primarily for fast naval vessels such as destroyers and frigates, where high speed and rapid power availability are more critical than fuel economy. While offering excellent performance and quick responsiveness, COGAG systems are mechanically complex, require precise control systems, and consume significantly more fuel than diesel-based alternatives.