Side view of Brunel's shield for boring the Thames tunnel. Marc Isambard Brunel (April 25, 1769 - December 12, 1849) was a French Engineer. In 1818 he patented a tunneling shield; a reinforced shield of cast iron in which miners would work in separate compartments, digging at the tunnel-face. His greatest achievement was the Thames Tunnel, an underwater tunnel, built beneath the River Thames connecting Rotherhithe and Wapping. It measures 35 feet wide by 20 feet high and is 1,300 feet long, running at a depth of 75 feet below the river's surface. It was the first tunnel known successfully to have been constructed underneath a navigable river, and was built between 1825 and 1843.