Although not strictly part of the Underground System, the Tower Subway was the world's first underground tube railway. Constructed using the revolutionary Greathead Shield invented by James Henry Greathead (used subsequently for many of the other tubes), the train (actually a single carriage) was cable operated and was effectively used as a shuttle service between the two banks of the Thames. The railway unfortunately was only open from August 2nd 1870 until November the same year due to very poor patronage.
The subway was not suitable for steam locomotives and opened with a carriage pulled on cables. Cable traction was not reliable and the experiment was abandoned after only a few months and the subway was converted to pedestrian usage. Despite being a major breakthrough in tunnelling technology, the venture (like Brunel's tunnel of 1843) was a financial failure. Greathead used the technique a few years later as engineer on the City of London and Southwark Subway (later the City and South London Railway), the world's first underground electric railway which opened in 1890