 Although some preparatory work was carried out , the outbreak of the Second World War in 1939 brought the electrification north of Rickmansworth to a halt . First class travel was abandoned by the LPTB , along with the Pullman cars , and the line was operated entirely as a shuttle service . In 1940 the Chesham branch was converted to <unk> working , in which the trains could be driven from each end , thus avoiding the time @-@ consuming repositioning of the locomotive . LNER C13 Class locomotives were used for this push @-@ pull working , along with two three @-@ car sets of antiquated Ashbury passenger cars dating from 1898 . 
