Parliament authorized the construction of the Tower Subway in 1868 and established the Tower Subway Company with three directors and starting capital of £12,000. Unfortunately, the trouble and expense incurred by the Thames Tunnel made contractors reluctant to take on the job. Finally, 24-year-old James Henry Greathead agreed to build it for £9,400. Together with Peter W. Barlow and Barlow’s son, Peter Barlow Jr., he designed and built the tunnel between 1869 and 1870, using a specially designed cylindrical wrought iron tunnelling shield, later known as the Barlow-Greathead shield.
The tunnel was originally designed to provide passenger service beneath the Thames, and when it opened on August 2, there was a small cable car capable of shuttling 12 passengers back and forth. The journey only took about 70 seconds, but the cramped, low-capacity car quickly proved uneconomical, and passenger service ceased after only three months. After that, the tunnel was converted into a pedestrian walkway, and it proved very popular. About a million people each year paid halfpenny each way to walk underneath the river.
Eventually, the subway was edged out by Tower Bridge, which was built a few hundred yards away and opened in 1894. Unlike the subway, the bridge was free, so there was no longer any incentive to use the subway to cross the river. Tower Subway finally closed in 1898. Since then, it’s been used as a route for hydraulic tubes, water mains, and, most recently, telecommunication cables.