, ▁former ▁chief ▁engineer ▁of ▁the ▁PR R , ▁was ▁appointed ▁as ▁Chief ▁of ▁Const ruction ▁and ▁Transport ation ▁in ▁the ▁Virginia ▁the ater . ▁The ▁depart ments ▁in ▁the ▁US MR R ▁t ended ▁to ▁operate ▁autonom ously , ▁although ▁mic rom an agement ▁from ▁the ▁Secretary ▁of ▁War ▁and ▁over la pping ▁authority ▁between ▁depart ments ▁did ▁affect ▁their ▁operations . ▁Over ▁time ▁the ▁US MR R ▁would ▁buy , ▁build ▁or ▁capture ▁ 4 1 9 ▁locomot ives ▁and ▁ 6 , 3 3 0 ▁cars ▁beyond ▁the ▁rolling ▁stock ▁that ▁was ▁requ is ition ed ▁from ▁the ▁various ▁Northern ▁rail ro ads . ▁When ▁Col . ▁Mc Call um ▁was ▁first ▁appointed ▁the ▁US MR R ▁system ▁consisted ▁only ▁of ▁ 7 ▁miles ▁of ▁the ▁Washington ▁and ▁Alexand ria ▁Rail road ; ▁however , ▁by ▁war ' s ▁end ▁the ▁US MR R ▁exerc ised ▁control ▁over ▁a ▁network ▁of ▁more ▁than ▁ 2 , 0 0 0 ▁miles ▁of ▁military ▁rail ro ads ▁and ▁captured ▁Southern ▁rail ▁lines . ▁ ▁Northern ▁Virginia : ▁ 1 8 6 2 ▁ ▁The ▁Virginia ▁Central ▁Rail road ▁and ▁Orange ▁and ▁Alexand ria ▁Rail road ▁were ▁the ▁principal ▁supply ▁lines ▁for ▁the ▁Confeder ate ▁and ▁Union ▁forces , ▁respectively . ▁ ▁G ett ys burg ▁Camp aign ▁ ▁Ch att ano oga ▁Camp aign ▁ ▁In ▁the ▁fall ▁of ▁ 1 8 6 3 ▁the ▁Confeder ate ▁rail ro ads , ▁acting ▁as ▁interior ▁lines ▁of ▁communication , ▁transferred ▁two ▁divisions ▁and