▁all ▁the ▁United ▁States ▁Military ▁Rail road ▁supplied ▁more ▁than ▁ 1 0 0 , 0 0 0 ▁troops ▁and ▁more ▁than ▁ 6 5 , 0 0 0 ▁horses ▁and ▁m ules ▁with ▁food , ▁equipment ▁and ▁supplies ▁from ▁the ▁water front ▁do cks ▁on ▁the ▁navig able ▁portion ▁of ▁the ▁James ▁River ▁at ▁City ▁Point . ▁ ▁Initial ▁rail road ▁operations ▁began ▁when ▁the ▁US MR R ▁re built ▁and ▁restored ▁service ▁along ▁ 9 ▁miles ▁of ▁the ▁Petersburg ▁and ▁City ▁Point ▁Rail road ’ s ▁line . ▁ ▁As ▁the ▁Union ▁Army ▁stead ily ▁extended ▁its ▁sie ge ▁lines ▁to ▁the ▁south ▁and ▁west , ▁the ▁US MR R ▁construction ▁corps ▁followed ▁in ▁the ▁Army ' s ▁w ake ▁extending ▁rail ▁service ▁from ▁City ▁Point ▁to ▁positions ▁behind ▁the ▁new ▁Union ▁left ▁fl ank . ▁ ▁Event ually ▁the ▁US MR R ▁added ▁ 2 1 ▁additional ▁miles ▁of ▁track ▁which ▁partially ▁enc irc led ▁Petersburg ▁from ▁the ▁east ▁to ▁the ▁south west . ▁ ▁Part s ▁of ▁the ▁US MR R ▁extension ▁are ▁preserved ▁today ▁within ▁the ▁borders ▁of ▁Fort ▁Lee , ▁Virginia , ▁where ▁a ▁series ▁of ▁four ▁historic ▁markers ▁show ▁the ▁route ▁that ▁the ▁rail road ▁followed ▁behind ▁the ▁Union ▁lines . ▁When ▁Petersburg ▁was ▁eventually ▁abandoned ▁in ▁ 1 8 6 5 ▁the ▁ 2 5 ▁engines ▁and ▁ 2 7 5 ▁pieces ▁of ▁other ▁rolling ▁stock ▁had ▁logged ▁a ▁grand ▁total ▁of ▁ 2 , 3 0 0 , 0 0 0 ▁operating ▁miles .