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Millions of people
Swarming like flies round
Waterloo Underground
- from Waterloo Sunset by The Kinks

The Waterloo & City line is famously the shortest remaining shuttle line on the London Underground, serving only two stations: Waterloo and Bank. It was constructed in 1898 to allow a train service to run under Central London from Waterloo rail station to the main business and banking area of the City of London. The London and South Western Railway company had wanted trains to run all the way from the south into City station¹ (renamed Bank in 1940), but the 1846 parliamentary ban on the building of surface lines in the City of London thwarted their plans. Instead, they enlisted the help of civil engineer WR Galbraith and the designer of the Greathead shield tunnelling device, James Henry Greathead, to build a deep-level line underneath London. Once the line was opened, the railway company could sell through-tickets to City station, with passengers changing from the surface line to the deep-level line at Waterloo station.

The line was bought out by Southern Railways in 1923, but was nationalised along with the mainline railways in 1948 and became part of the London Underground in 1994 when it was bought for the nominal fee of £1. The railway has been managed by Metronet since 2003 as part of the Underground's Public-Private Partnership scheme, and is constantly being worked on to reduce its current unreliability. The line between the two stations is only 1.5 miles² long, so it takes just four minutes for trains to traverse it. Both the line and its small Waterloo depot are entirely underground.

Known colloquially as 'the Drain', The Waterloo & City line now carries over ten million passengers each year, with trains running every three minutes at peak times. The line is notable for the fact that the trains always stop at the same point in each station, allowing commuters to stand next to where the doors of the train will be when it arrives. The line has always been closed on Sundays, except for a brief period between 1943 and 1947. Nowadays, Sundays are often used for filming, and the line features in both Sliding Doors and the BBC TV serial The Tripods.

Structure

At Bank, the line is connected to the main station by a tunnel with a moving walkway which leads onto one of the two island platforms. The Waterloo & City line is isolated from the underground walkway which links Bank and Monument stations, and so those changing for the other lines at Bank³ and Monument⁴ must do so via the Bank station ticket hall. The line begins by running west towards Blackfriars, but then curves southwards to cross under the river Thames. After this it curves back towards the west to head straight towards Waterloo and then curves southwards into the station. The platforms at Waterloo lie on either side of the pair of tracks, as the concrete pillars supporting the mainline station above leave no room for an island platform. This means that the doors open on the opposite side to that at Bank. The line at Waterloo can be most easily reached via the steps down from the subway that runs under the mainline platforms, but passengers can reach the line from any of the entrances from the mainline station. The station is also served by the Northern, Bakerloo and Jubilee lines.

A small depot lies to the south of the platforms at Waterloo, but there is no direct access to the surface and trains must be lowered, carriage by carriage, down from Waterloo mainline station. The line ran wooden trains until these were replaced in 1940 with electric multiple units⁵, which lasted until they were replaced by the line's current 1992-stock four-car trains in 1994⁶. At each change, the old trains were winched out and the new ones lowered down onto the line. The line was closed for five months in 2006 to allow refurbishment of the line and replacement of the tracks and electrical systems, with the trains being cleaned and repainted in the official Underground colours.