General Burnside, soon after assuming command, and while waiting at Warrenton, made a radical change in the organization of the army by consolidating the corps into three “Grand Divisions” as follows:
The Right Grand Division, General Sumner commanding.—Second Army Corps, General D. W. Couch; Ninth Army Corps, General O. B. Wilcox.
Centre Grand Division, General Joseph Hooker commanding.—Third Army Corps, General George Stoneman; Fifth Army Corps, General Daniel Butterfield.
Left Grand Division, General W. B. Franklin commanding.—First Army Corps, General J. F. Reynolds; Sixth Army Corps, General W. F. Smith.
Cavalry Division.—General Alfred Pleasonton.
Artillery, siege, and field batteries, 370 guns, General Henry J. Hunt, Chief.
At the time of the change of commanders the Confederates were looking for a Federal move north of Culpeper Court-House, and were surveying the ground behind Robertson River for a point of concentration of the two wings to meet that move.
General Burnside, however, promptly planned operations on other lines. He submitted to President Lincoln his proposition to display some force in the direction of Gordonsville as a diversion, while with his main army he would march south, cross the Rappahannock at Fredericksburg, and reach by a surprise march ground nearer Richmond than the holdings of the Confederates. This was approved by the President with the suggestion that its success depended upon prompt execution.
On the 15th light began to break upon the Confederates, revealing a move south from Warrenton, but it was not regarded as a radical change from the Orange and Alexandria Railroad line of advance. A battery of artillery was sent with a regiment of infantry to reinforce the Confederate outpost at Fredericksburg under Colonel Ball.
On the 17th information came that the Right Grand Division under General Sumner had marched south, leaving the railroad, and General W. H. F. Lee’s cavalry was ordered to Fredericksburg.