The Class 487 Electric Multiple Units were unique on the British Railways / British Rail network in that their revenue service was spent entirely underground. They ran the Waterloo & City Line which nowadays is part of London Underground but originally the 1 and a half mile long line between Waterloo and the City of London was separate and operated by a succession of mainline railway companies until the advent of nationalisation and British Rail. In 1994 the line was transferred to LU to become a "tube" proper.
The O.V.S. Bulleid designed Class 487s were built for the Southern Railway during WW2 and entered service from 1940. The units consisted of driving motor cars (with cabs at both ends - and hence could operate singly) and trailers. In off-peak periods the Waterloo & City Line trains often ran with just a pair of motor cars while in peak times 3 trailers were usually marshalled between 2 motor cars.
They remained in service until being replaced by the Class 482 in 1993 seeing out their final days in Network South East livery no less. The Class 487s operated on 660v DC third rail and spent all of their working lives on their short underground line though they did see sunlight now and then when they needed heavy maintenance and had to be bought up to the surface. For test purposes one driving car operated above ground in the late 1970s for a short period.
One DMBSO driving car has been saved from the scrap man and is being restored at the London Transport Museum. It will be restored to Network South East livery.