London Underground battery-electric locomotives

London Underground battery-electric locomotives are battery locomotives used for hauling engineers' trains on the London Underground network, where they can run when the electric traction current is switched off. The first two were built in 1905 for the construction of the Great Northern, Piccadilly and Brompton Railway, and the District Railway bought two more in 1909. Later vehicles were first made by converting redundant motor cars, and from 1936 battery locomotives were built as new vehicles, often reusing refurbished bogies and motors. By 1986, 52 machines had been built in six batches from four manufacturers, with one built at London Transport's Acton Works. Eleven ordered in 1972 were built at Doncaster Works by British Rail Engineering Limited and delivered in 1973; their motors were refurbished from redundant District line stock but the bogies were new.