The geared steam turbine plant was the heart of virtually every major US Navy combatant built between the two World Wars and through World War II. Battleships, cruisers, carriers, and destroyers alike relied on high-pressure superheated steam — generated in oil-fired boilers at pressures of 300 to 600 psi and temperatures reaching 850°F — to spin turbines driving the ship’s propeller shafts. The photographs below show the principal components of a typical naval propulsion plant: the double-reduction gear, the high-pressure turbine, and the low-pressure turbine.
Steam enters the high-pressure (HP) turbine first, expanding through multiple stages of blades to extract the bulk of the available energy. The partially expanded steam exhausts from the HP turbine and passes directly to the low-pressure (LP) turbine, where it expands further through additional blade stages before exhausting to the main condenser. This two-turbine arrangement extracts the maximum energy from each pound of steam and allows each turbine to be optimized for its pressure range. Cruising turbines were often incorporated into the LP casing for fuel economy at reduced speed, allowing the HP turbine to be shut off entirely on long passages.
Because steam turbines operate most efficiently at very high shaft speeds — typically 3,000 to 6,000 revolutions per minute — while propellers require far lower speeds (200–300 rpm) to work efficiently, a reduction gear couples the turbines to the propeller shaft. The double-reduction gear shown here uses two stages of helical gearing to step the turbine speed down to shaft speed, transmitting thousands of horsepower while keeping the gear set compact enough to fit within the engineering spaces. Precision-cut helical gears, running in an oil-flooded housing, made the double-reduction gear one of the most demanding precision manufacturing tasks of the wartime shipbuilding program.
Reduction Gear
High-Pressure Turbine
HP Turbine Exhaust to LP Turbine
Low-Pressure Turbine
