Combined steam and gas (COSAG) is a
propulsion system for
ships using a combination of
steam turbine
A steam turbine is a machine that extracts thermal energy from pressurized steam and uses it to do mechanical work on a rotating output shaft. Its modern manifestation was invented by Charles Parsons in 1884. Fabrication of a modern steam turbin ...
s and
gas turbines to power the
shafts. A
gearbox and
clutch
A clutch is a mechanical device that engages and disengages power transmission, especially from a drive shaft to a driven shaft. In the simplest application, clutches connect and disconnect two rotating shafts (drive shafts or line shafts). ...
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 and .
The also used it.
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Marine propulsion
Steam power