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Desire for higher power

The dawn of gas turbine locomotives

The application of gas turbines to the prime mover of locomotive began shortly after the modern gas turbine had been produced. Brown Boveri built the first gas turbine locomotive in 1941, with 2000 hp electric drive. This locomotive was operated in Switzerland and tested for the long duration.
The turbine inlet temperature  of this engine was about 600 degrees C and the thermal efficiency was about 19%, better than that of reciprocating steam but much worse than diesel. But the gas turbine locomotive showed much potential for a high power locomotive.

Under development

 After the WW2, many researches of gas turbine locomotives were actively done in US and Europe. In the United States, Union Pacific produced 4500 hp prototype turbine electric locomotive in 1948 and then 25 mass production type were produced.
In England, 2500 hp locomotive in 1950 and in French, 1000 hp free piston direct drive locomotive was produced in 1952. In Soviet Union, 6000 hp direct drive and electric drive locomotives were tested.

At its peak

 The intercontinental railroad, Union Pacific operated the high power steam locomotive nicknamed Big Boy, whose output at rim exceeded 6000 hp and weighed about 500 metric tons. In those days diesel electric locomotives could achieve only 2000 hp (1400 hp at rim) and could not replace Big Boys..

 Union Pacific decided to replace Big Boys with high power gas turbine locomotives. For this purpose, 8500 hp gas turbine electric locomotives were produced. They were the most powerful internal combustion locomotive build in 20th century. One locomotive consisted of three cars, first was the motive car with the auxiliary diesel generator, second was the motive car with the turbine generator, third was the fuel tender with the heating apparatus to utilize the highly viscous bunker C oil as a fuel. This 87000 liters tender compensated for the turbine's low efficiency to expand the cruising distance. Turbines in those days consumed much fuel due to low efficiency, roughly twice as much fuel as a diesel. To reduce the fuel consumption, the engine was stopped while descending a long down grade. A diesel generator was on board to maintain the mobility when the turbine stopped, but the output was not enough to haul the total train mass.
The fuel of these locomotive was bunker C oil, highly viscous heavy oil. In those days bunker C was considered waste and very cheap. As the turbine inlet temperature was low, the turbine blade damage was a little even if such a low quality sulfur rich fuel was used. 30 locomotives were being build and actively used in hill climbing and heavy freight services.

DB (German National Railways) used gas turbine as an auxiliary power source, because a high power non-electric locomotive was not needed. 2500 hp diesel was used as a prime mover and 1200 hp light weight gas turbine was used to boost up the total performance.

6000 hp turbine electric locomotive and direct drive locomotive were being built in Soviet Union, and China also built a turbine electric locomotive.

Counterattack of diesel

Diesel locomotives were growing more powerful and more efficient in 70's to 80's. In the United States, single locomotive achieved the output of 6600 hp, and 3000 hp in Europe. 
In Union Pacific, there was a substantial increase in freight transport and more power was required. To achieve 10000 to 20000 horse power, two or three fuel efficient modern high power diesel locomotives were coupled and replaced the turbine locomotive.