To design the railway, the CLR employed the engineers James Henry Greathead, Sir John Fowler, and Sir Benjamin Baker. Greathead had been the engineer for the Tower Subway and the C&SLR, and had developed the tunnelling shield used to excavate those companies' tunnels under the River Thames. Fowler had been the engineer on the Metropolitan Railway, the world's first underground railway opened in 1863, and Baker had worked on New York's elevated railways and on the Forth Railway Bridge with Fowler. Greathead died shortly after work began and was replaced by Basil Mott, his assistant during the construction of the C&SLR.