Thomas A. Scott, vice-president of the Pennsylvania Railroad (PRR), served as an Assistant Secretary of War during the period 1861–1862.

[6] Over time the USMRR would buy, build or capture 419 locomotives and 6,330 cars[1] beyond the rolling stock that was requisitioned from the various Northern railroads.

In the fall of 1863 the Confederate railroads, acting as interior lines of communication, transferred two divisions and an artillery battalion of Lieutenant General James Longstreet’s I Corps, Army of Northern Virginia, by railroad from Virginia to Georgia to reinforce General Braxton Bragg’s Army of Tennessee.

Major General William T. Sherman, with 4 divisions of the Army of the Tennessee, was already moving east from the vicinity of Vicksburg, Mississippi and expected to arrive in about 10 days.

[12] Stanton proposed that reinforcements be sent from the then idle Army of the Potomac, his initial recommendation was to move 30,000 troops in just 5 days to the vicinity of Bridgeport, Alabama.

[14][17][18] The men at the conference worked out the detailed route planning, a task complicated by the different gauges of railroad track in use at the time.

[23] While the railroad men planned the movement of reinforcements to the west, Halleck began issuing the orders that assigned actual units to the move.

Major General George Meade, the commander of the Army of the Potomac, was directed to prepare the XI and XII Corps for movement beginning September 25.

The XI Corps’ remaining two divisions were deployed to the army's rear guarding the Orange and Alexandria railroad which simplified their preparations to move.

On September 27 the railroads began loading the camp baggage, wagons, ambulances, horses and mule teams that were part of the corps.

The Union did not capture Petersburg before the city's defenders were reinforced by troops from General Lee's Army of Northern Virginia.

Eventually the USMRR added 21 additional miles of track which partially encircled Petersburg from the east to the southwest.

[32] Parts of the USMRR extension are preserved today within the borders of Fort Gregg-Adams, Virginia, where a series of four historic markers show the route that the railroad followed behind the Union lines.

[34] When Petersburg was eventually abandoned in 1865 the 25 engines and 275 pieces of other rolling stock had logged a grand total of 2,300,000 operating miles.