Most of the tunnels for the extensions to the east of London had been built by 1940, but work slowed due to the outbreak of the Second World War until eventually suspended in June.
Det meste af tunnellerne for forlængelsen til det østlige London var blevet bygget i 1940, men arbejdet gik langsommere pga. 2. verdenskrigs udbrud og sidenhen suspenderet i juni.