The core of a turbine is a shaft with several series of blades set along its length. The shaft is surrounded by a casing, which also has rows of blades, which come between the rows on the shaft. Steam from a boiler is admitted to the space between the casing and the shaft. As it flows over the blades, the steam turns the shaft. It is the reverse of a propellor: the flowing steam moves the blades which rotate the shaft.

Turbines have the advantages of being much more compact than a reciprocating engine, and being able to turn at much higher speeds. Indeed, the problem with early turbines was the opposite of that with reciprocating steam engines: the speed the shaft rotated was too great for the screws, and it had to be geared down.

Unprecedented speeds

Steam turbines were employed in small and large passenger vessels, including cross channel ferries and Atlantic liners. Navies also made great use of them to drive warships at higher speeds than were previously possible. Indeed, the turbine allowed unprecedented power to be built into merchant ships and warships. Turbine-propulsion made possible the fastest and biggest Atlantic liners, for instance the Queen Mary, Queen Elizabeth, Normandie and United States.