These include battery locomotives, diesel locomotives, electric locomotives, sleet locomotives, pilot motor cars and ballast motor cars.
Pilot motor cars and ballast motor cars are generally vehicles which have been withdrawn from passenger service, but continue to be used by the engineering department.
The first ballast motor cars were former trailer cars built for the Central London Railway in 1900, which were converted to motor cars for trials of the first multiple system to be used in Britain, and were retained for departmental use after 1903.
Four Hungarian-built gate stock motor cars were used as ballast motor cars, and were numbered L13 to L16.
Deliveries of 1972 stock enabled 1938 stock to be withdrawn, and several cars were converted for use as ballast motor cars.
The next batch of ballast motor cars were French-built gate stock cars, originally constructed in 1906, but converted in the early 1920s to run with the 1920 air-door stock.
Although 12 of the displaced cars were scrapped, six were kept as ballast motor cars, becoming numbers L24 to L29 in the service fleet.
In 1953, fourteen standard stock motor cars were withdrawn from passenger service, and were converted to ballast motor cars, with the final one completed in early 1955.
Pilot motor cars are used to move other vehicles around the system, while ballast motor cars are used to haul ballast trains and engineering trains.
Two of the trial cars, numbers 201 and 202, were retained and became the first ballast motor cars to work on the Underground.
Although the ballast motor cars were normally worked in pairs, some engineering trains had a ballast motor car at one end and a battery locomotive at the other.
