urban ▁network , ▁called ▁the ▁Berliner ▁Stadt -, ▁Ring ▁und ▁Vor ort bah nen ▁( Ber lin ▁City -, ▁Circ ular ▁and ▁Sub urban ▁lines , ▁renamed ▁to ▁S - B ahn ▁in ▁December ▁ 1 9 3 0 ), ▁since ▁the ▁original ▁establishment ▁of ▁a ▁special ▁sub urban ▁tar iff ▁in ▁ 1 8 9 1 . ▁The ▁Nau en ▁sub urban ▁line , ▁together ▁with ▁the ▁W ust erm ark ▁sub urban ▁line , ▁terminated ▁at ▁the ▁Berlin ▁Lehr ter ▁Bahnhof , ▁just ▁like ▁the ▁long ▁distance ▁trains ▁of ▁the ▁same ▁lines . ▁ ▁The ▁Nau en ▁and ▁W ust erm ark ▁lines ▁were ▁the ▁only ▁sub urban ▁lines ▁of ▁the ▁Berlin ▁S - B ahn ▁which ▁had ▁not ▁been ▁elect r ified ▁before ▁the ▁ 2 nd ▁World ▁War . ▁The ▁part ▁from ▁Fal ken see ▁to ▁the ▁Northern ▁Ring ▁line ▁was ▁elect r ified ▁with ▁Third ▁Rail ▁in ▁ 1 9 5 1 , ▁being ▁oper ational ▁from ▁August ▁ 1 4 , ▁ 1 9 5 1 ▁to ▁the ▁end ▁of ▁the ▁ 1 9 5 0 s , ▁thus ▁en abling ▁direct ▁S - B ahn ▁trains ▁from ▁East ▁Berlin ▁to ▁the ▁places ▁being ▁located ▁in ▁the ▁G DR ▁west ▁of ▁Sp and au . ▁ ▁After ▁the ▁construction ▁of ▁Berlin ▁Wall ▁on ▁ 1 3 ▁August ▁ 1 9 6 1 , ▁this ▁link ▁was ▁also ▁sever ed . ▁Fal ken see ▁and ▁the ▁Hav ell and ▁( Ber lin ’ s ▁north western ▁out sk