The Waterloo & City line is a short, fully underground railway line in central London, England. Part of the London Underground rapid transit network, it operates as a shuttle service between Waterloo and Bank stations with no intermediate stops.
The line was built by the Waterloo & City Railway Company and opened for service on 11 July 1898 (at the time, Bank station was named "City"). When it opened it was the second electric tube railway in London, after the City and South London Railway (now part of the Northern line). For much of its existence, it was owned and operated by two mainline rail companies, before it was nationalised into British Rail. Operations were transferred to London Underground in 1994 following a major refurbishment and replacement of rolling stock.
The Waterloo & City line is by far the shortest line on the entire London Underground network, with a line length of 2.37 km (1.47 miles), and an end-to-end journey lasting just four minutes. In absolute terms, it is the least used line on the network, carrying just over 15 million passengers annually. However, in terms of the average number of journeys per mile, it is the second most intensively-used line, behind only the Victoria line. wikipedia