What was Londons first underground?

Answer 1

The first underground railway in London ran from what is now Paddington Bishop's Road (officially Paddington Suburban or Paddington (H&C)) and to Farringdon along the current route of Hammersmith and City. This was more of a railway than an underground line though, as it was served by steam trains. The first proper underground railway in it's modern definition (small, almost circular tunnels) was ran by City & South London Railway between Stockwell and King William Street. King William Street is now closed, but it was near current Bank station. The C&SLR trains ran along Northern Line's current tracks, except between London Bridge and King William Street, where there was another set of tracks. The King William Street tracks were disconnected from the network when C&SLR was extended north to Angel.