▁class ▁Pacific s ▁for ▁the ▁Spirit ▁of ▁Progress ▁express , ▁and ▁the ▁single ▁ 4 - 8 - 4 ▁H ▁class ▁locomot ive ▁H 2 2 0 , ▁the ▁biggest ▁Victor ian ▁Rail ways ▁steam ▁locomot ive . ▁The ▁final ▁steam ▁locomot ives ▁built ▁for ▁the ▁Victor ian ▁Rail ways ▁were ▁the ▁ 4 - 6 - 4 ▁R ▁class ▁and ▁ 2 - 8 - 0 ▁J ▁classes . ▁Although ▁they ▁were ▁of ▁more ▁modern ▁design , ▁their ▁advantages ▁were ▁over shadow ed ▁by ▁the ▁simultane ous ▁arrival ▁of ▁the ▁first ▁dies els . ▁ ▁Electric ▁locomot ives ▁were ▁first ▁acquired ▁with ▁the ▁elect r ification ▁of ▁the ▁sub urban ▁rail ways , ▁the ▁E ▁class ▁sub urban ▁engines ▁acquired ▁in ▁ 1 9 2 3 ▁and ▁ 1 9 2 8 – 2 9 , ▁followed ▁by ▁the ▁L ▁class ▁from ▁ 1 9 5 3 ▁when ▁the ▁main line ▁to ▁Tr ar alg on ▁was ▁elect r ified ▁for ▁b ri qu ette ▁traffic . ▁ ▁Dies el isation ▁occurred ▁from ▁ 1 9 5 1 ▁with ▁the ▁F ▁class ▁sh unter , ▁but ▁the ▁B ▁and ▁S ▁classes ▁of ▁ 1 9 5 2 ▁and ▁ 1 9 5 7 ▁revolution ised ▁main ▁line ▁operations . ▁They ▁were ▁then ▁followed ▁by ▁the ▁T ▁and ▁Y ▁classes ▁in ▁ 1 9 5 5 ▁and ▁ 1 9 6 3 ▁which ▁disp la ced ▁steam ▁from ▁the ▁branch ▁lines ▁and ▁yards . ▁A part ▁from ▁the ▁F ▁class , ▁C ly