James Henry Greathead (6 August 1844 – 21 October 1896)[1] was an English 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.

[4] 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.

Soon after, in 1869, he rejoined Barlow and they began work on designs for the Tower Subway,[5] only the second tunnel to be driven under the river Thames in central London.

[6] Barlow had been awarded a provisional patent on his second idea but Greathead was unaware of this until several years later (as discussed in minutes of a meeting of the Institution of Civil Engineers (ICE) published in January 1896).

"[12] Whilst Barlow patented his idea in 1864, in 1869 both Greathead in England and Beach in New York practically simultaneously constructed their own shields that were similar but independent of each other.

Minutes in the ICE library suggest Barlow quietly patented his ideas for a cylindrical cutting shield but never built one.

According to a 2017 video lecture given by Professor Lord Mair for the ICE, the Brunels' shield ideas were well known in both USA and UK.

Since Portland cement had only been invented in 1824 by Joseph Aspdin of Leeds, it was not fully appreciated by the construction industry for many years.

It was only because of Portland cement's hydraulic properties and ability to set in wet environments that these first tunnel ventures under the Thames came to fruition at all.

In use, the shield was inched forward as the working face was excavated, while behind it a permanent tunnel lining of cast iron segments was fitted into place, itself an important innovation.

[15] Greathead patented many of his ideas including the use of compressed air and forward propulsion by hydraulic jacks, both of which are now standard features of tunnel construction.