This film is about the introduction of automated computerised train control on the London Underground Subsurface Railway (SSR) network the lines where most of the subterranean sections of railway were built as 'cut and cover' in the steam train era.

Automation is part of the Four Lines Modernisation project (4LM) which includes the Metropolitan, District, Circle and Hammersmith & City Lines.

Also seen in this film are the routes jointly operated (with other services) where 'interoperable signalling' will allow humans to continue driving trains not being automated and how heritage train operations could continue.