James Henry Greathead was a mechanical and civil engineer renowned for his work on the London Underground railways, Winchester Cathedral, and Liverpool overhead railway, as well as being one of the earliest proponents of the English Channel, Irish Sea and Bristol Channel tunnels.
Using his ‘Greathead Shield’, the engineer James Henry Greathead was instrumental in the building of the London Underground. James Henry Greathead, a British civil engineer who improved the tunneling shield, the basic tool of underwater tunneling, essentially to its modern form.
Born in Grahamstown, South Africa. He was educated at St. Andrew’s College, Grahamstown, and the Diocesan College private school in Cape Town. After emigrating to England in 1859, he completed his education from 1859 to 1863 at the Westbourne Collegiate School, Westbourne Grove. At the age 15,he returned briefly to South Africa before finally moving to London in 1864 to serve a three-year pupillage under the civil engineer Peter W. Barlow, from whom he became acquainted with the rectangular shield system of tunnelling

In 1869, aged only 24, Greathead was entrusted with the construction of the Tower Subway, a pedestrian tunnel under the Thames. Completed in 1870, it was built using a cylindrical boring device designed by Greathead that enabled tunnels to be driven through soft, waterlogged ground. He continued to develop this machine, which became known as the ‘Greathead Shield’.

The tunneling shield invented by Marc Isambard Brunel and used to build the Thames Tunnel was large and unwieldy. Barlow designed a smaller shield, circular in cross section, which Greathead modified to complete the Tower Subway (1869) under the River Thames near the Tower of London. As the shield was pushed forward by screw jacks, the tunnel behind it was lined with cast-iron rings.
In 1886 Greathead began work to carry the City and South London Railway under the Thames near London Bridge, using a larger version of his shield, with which he bored twin tunnels about 10 feet (3 metres) in diameter. In this project he pioneered the use of compressed air in conjunction with the circular shield. His shield, compressed air, and the cast-iron rings used to line the tunnels came to be adopted generally in tunnel construction.