18000 was a prototype mainline gas turbine locomotive built for British Railways in 1949 by Brown Boveri. It had, however, been ordered by the Great Western Railway in 1940, but construction was delayed due to World War II. It spent its working life on the Western Region, operating express passenger services from London Paddington.

It was of A1A-A1A wheel arrangement and its gas turbine was rated at 2500hp. It had a maximum speed of 90mph and weighed 115tons. It was painted in BR black livery, with a silver stripe around the middle of the body and silver numbers.

At the end of 1960 it was withdrawn from operation and was stored at Swindon Works for four years. It was then sold back to Brown-Boveri, who returned it to Switzerland in January 1964 where it was used for testing. In the early 1990s it was secured for preservation and returned to the United Kingdom, and is now kept at the Railway Age, Crewe.