 The line opened to passengers on 31 July 1936 , less than 12 weeks after construction began . It was formally opened by Lieutenant @-@ Colonel Edwin Charles Cox , Traffic Manager of the Southern Railway , who commented that as the traffic manager of what was then the largest electric rail service in the world , he was now opening what was probably the smallest . Initially , the tunnel was decorated with illuminated scenes depicting Switzerland , Canada , the Netherlands , Japan and Egypt . 
