Combined steam and gas (COSAG) is a propulsion

Marine propulsion

Marine propulsion is the mechanism or system used to generate thrust to move a ship or boat across water. While paddles and sails are still used on some smaller boats, most modern ships are propelled by mechanical systems consisting a motor or engine turning a propeller, or less frequently, in jet...

 system for ship

Ship

Since the end of the age of sail a ship has been any large buoyant marine vessel. Ships are generally distinguished from boats based on size and cargo or passenger capacity. Ships are used on lakes, seas, and rivers for a variety of activities, such as the transport of people or goods, fishing,...

s using a combination of steam turbine

Steam turbine

A steam turbine is a mechanical device that extracts thermal energy from pressurized steam, and converts it into rotary motion. Its modern manifestation was invented by Sir Charles Parsons in 1884....

s and gas turbine

Gas turbine

A gas turbine, also called a combustion turbine, is a type of internal combustion engine. It has an upstream rotating compressor coupled to a downstream turbine, and a combustion chamber in-between....

s to power the shafts. A gearbox

Transmission (mechanics)

A machine consists of a power source and a power transmission system, which provides controlled application of the power. Merriam-Webster defines transmission as: an assembly of parts including the speed-changing gears and the propeller shaft by which the power is transmitted from an engine to a...

 and clutch

Clutch

A clutch is a mechanical device which provides for the transmission of power from one component to another...

es enable either of the engines or both of them together to drive the shaft. It has the advantage of the cruising efficiency and reliability of steam and the rapid acceleration and start-up time of gas. This system was mainly used on first-generation gas-turbine ships such as the Royal Navy's

Royal Navy

The Royal Navy is the naval warfare service branch of the British Armed Forces. Founded in the 16th century, it is the oldest service branch and is known as the Senior Service...

 County class destroyer

County class destroyer

The County class was a class of guided missile destroyers, the first such vessels built by the Royal Navy. Designed specifically around the Sea Slug anti-aircraft missile system, the primary role of these ships was area air-defence around the aircraft carrier task force in the nuclear-war...

 and Tribal class frigate

Tribal class frigate

The Type 81, or Tribal class, was a class of seven general-purpose frigates for the Royal Navy designed during the 1950s that served throughout the 1960s and 1970s with limited service during the 1980s.-History:...

 .

The Spanish aircraft carrier Dédalo

Spanish aircraft carrier Dédalo

Dédalo was the first Spanish aircraft carrier and the second aviation ship in the Spanish Navy . She remained the fleet's flagship until the Principe de Asturias replaced her...

also used it.