Who designed the first tunnel under a navigable river?

Marc Isambard Brunel designed the first successfully completed tunnel beneath a navigable river, the Thames Tunnel in London.

Brunel proposed the tunnel between Rotherhithe and Wapping and patented his tunnelling shield in 1818. The shield supported the surrounding soft, waterlogged ground while workers excavated small sections and built a brick lining behind them. This method made an underwater crossing possible where earlier attempts had repeatedly flooded or collapsed.

Construction began in 1825 and was finally completed in 1843 after serious floods, financial interruptions and years of delay. Marc Brunel's son, Isambard Kingdom Brunel, served as an assistant and later became closely associated with the project, which explains the frequent confusion between the two names. The father was the principal designer and engineer; the son helped oversee construction and emergency work.

The Thames Tunnel was intended for wheeled traffic but opened mainly as a pedestrian tunnel. In 1869 it became part of a railway route. It is often described as the first successful tunnel under a navigable river, although ancient claims about a possible Euphrates tunnel make absolute “first ever” wording less certain.