British Rail 18000 was a prototype mainline Gas turbine-electric locomotive built for British Railways in 1949 by Brown , Boveri & Cie. It had , however , been ordered by the Great Western Railway in 1940 , but construction was delayed due to World War II . British Rail 18000 was a prototype mainline gas turbine-electric locomotive built for British Railways in 1949 by Brown , Boveri & Cie. It had , however , been ordered by the Great Western Railway in 1946 , but construction was delayed due to World War II .