▁trains ▁an ▁hour . ▁ ▁Progress ▁of ▁works ▁Work ▁began ▁in ▁the ▁late ▁ 1 9 3 0 s , ▁and ▁was ▁in ▁progress ▁on ▁all ▁front s ▁by ▁the ▁out break ▁of ▁World ▁War ▁II . ▁The ▁t unn elling ▁north wards ▁from ▁the ▁original ▁High gate ▁station ▁( now ▁Arch way ) ▁had ▁been ▁completed , ▁and ▁the ▁service ▁to ▁the ▁re built ▁surface ▁station ▁at ▁East ▁Fin ch ley ▁started ▁on ▁ 3 ▁July ▁ 1 9 3 9 , ▁but ▁without ▁the ▁opening ▁of ▁the ▁intermediate ▁( new ) ▁High gate ▁Station , ▁at ▁the ▁site ▁of ▁the ▁L NER ' s ▁station ▁of ▁the ▁same ▁name . ▁Further ▁progress ▁was ▁dis rupted ▁by ▁the ▁start ▁of ▁the ▁war , ▁though ▁enough ▁had ▁been ▁made ▁to ▁complete ▁the ▁elect r ification ▁of ▁the ▁High ▁Bar net ▁branch ▁on wards ▁from ▁East ▁Fin ch ley ▁over ▁which ▁t ube ▁services ▁started ▁on ▁ 1 4 ▁April ▁ 1 9 4 0 ; ▁the ▁new ▁( deep - level ) ▁High gate ▁station ▁opened ▁on ▁ 1 9 ▁January ▁ 1 9 4 1 . ▁The ▁single ▁track ▁L NER ▁line ▁to ▁Ed g ware ▁was ▁elect r ified ▁as ▁far ▁as ▁Mill ▁Hill ▁East , ▁including ▁the ▁D oll is ▁Brook ▁Vi ad uct , ▁opening ▁as ▁a ▁t ube ▁service ▁on ▁ 1 8 ▁May ▁ 1 9 4 1 ▁to ▁serve ▁the ▁bar ra cks ▁there , ▁thus ▁forming ▁the ▁Northern ▁line ▁as ▁it ▁is ▁today . ▁The