The Tube's shortest line has reopened after five months, following a major upgrade of track and equipment.
Journeys on the Waterloo & City line will be quicker following the upgrade
The Waterloo and City line, nicknamed The Drain, has two stops and carries an average of 37,000 commuters a day.
Maintenance firm Metronet promised faster journeys, more room, CCTV in every carriage and better reliablity.
The line was supposed to re-open on 1 September but engineering works overran - Metronet will be fined hundreds of thousands of pounds for the delay.
Trains are newly refurbished and have been painted in London Underground's distinctive red, white and blue livery.
A spokesperson for London Underground said the upgrading work was a bit behind but that it was "a complex project requiring a great deal of work".
LU's Tim O'Toole said: "We look forward to a safer, more reliable and comfortable Waterloo & City line and for Metronet to continue to deliver improvements to the Tube, as promised."
The upgrade of the Waterloo & City line is part of Transport for London's £10bn investment programme to improve and expand London's transport network.