After World War II, extensive research in combustion engineering aided the development of turbine-electric locomotives, in which either gas or steam turbines were used to drive generators powering electric motors.
A boiler was required to produce the steam in a steam turbine. In the gas turbine, gas was produced in a combustion chamber directly ahead of the turbine wheel. Either coal or oil may be used as fuel to produce steam or gas for turbine operation. Liquid propane gas has been used experimentally as fuel for gas turbines.
All of these types of turbine-powered locomotives have been judged to be uneconomical for general freight rail operations. Only the gas turbine, driving wheels through hydraulic transmission, has continued in service in the 1990s as the motive power in the form of a power car hauling a lightweight passenger train.