It was a public transport revolution. London had led the world in the development of a subterranean railway system. The first sub-surface lines, constructed by the cut-and-cover method, were operated with steam locomotives. In theory the tunnels and stations were ventilated into the outside air, but in practice they became dingy, miserable, smoke-filled spaces. As one early traveller recorded in his journal, `I had my first taste of Hades today ...the atmosphere was a mixture of sulphur, coal dust and foul fumes`. The railway companies desperately needed to clean up their act. It was only with the arrival of exhaust-free electric traction - combined with improvements to the tunnelling shield, pioneered by Sir Marc Brunel - that the engineers were able to tunnel far deeper to create London`s `Tube` system. Graeme Gleaves traces the development of the Underground from the early years and through the introduction and development of the electrified system