September 29, 1863 – General Robert E. Lee began planning to attack after receiving confirmation that Major General George G. Meade’s Federal Army of the Potomac was weakened.
Confederates in the front lines along the Rapidan River in northern Virginia could hear trains pulling in and out behind the Federal lines. Lee had received reports that some Federal troops, possibly XI and XII corps under Major Generals Oliver O. Howard and Henry W. Slocum respectively, were leaving the army. But the presence of new Federal pickets on the riverbank indicated to Lee that Meade had been reinforced.
New information then arrived at Lee’s headquarters from the Shenandoah Valley, which Lee forwarded to President Jefferson Davis with an added message: “It is stated that Generals Slocum and Howard’s corps, under General (Joseph) Hooker, are to re-enforce General (William) Rosecrans (at Chattanooga). They were to move over the Baltimore and Ohio Railroad, and to commence on the night of the 25th.”
Lee doubted this report’s authenticity since his cavalry “still closely guarded” the railroad, but, “If the report from the valley is true, it will no doubt be corroborated to-day or to-morrow.”
The notion of two Federal corps leaving Meade’s army concerned Lee in two ways. First, it “furnishes additional reason for prompt action on the part of General (Braxton) Bragg” (at Chattanooga), if those corps were indeed going to reinforce Rosecrans. Second, “if the withdrawal of these two corps under General Hooker is true, they may be intended to operate on the Peninsula as a diversion to Meade’s advance.”
On the 29th, Lee received another report stating that Federal troops were heading west. This came from Major Harry Gilmore, commanding Confederate cavalry at Newtown, Virginia. Gilmore correctly identified both XI and XII corps as the Federals on the move, as well as Hooker being their new commander. Lee wrote Davis, “The report has been repeated from valley without giving the circumstances on which it was based.”
However, Lee received more conflicting reports from scouts north of the Rappahannock River stating that Meade was being reinforced. Lee wrote, “Those on the Potomac report a large steamer laden with troops as having passed up the river on the 21st, one on the 22d, one on the 23d, and two on the 25th,” even though they “may have been conscripts.”
By this time, Lee had begun leaning toward the theory that Meade was losing troops to Rosecrans. Lee wrote, “If it is true that re-enforcements are being sent from General Meade to General Rosecrans, it shows that the enemy is not as strong as he asserts.”
Regarding the Chattanooga situation, Lee shared reports “that (General Ambrose) Burnside (at Knoxville) has carried nearly all his troops to re-enforce Rosecrans, leaving only a brigade or two of mounted men between him and Knoxville.” It was also “probable” that part of Major General Ulysses S. Grant’s Army of the Tennessee was heading east to reinforce Rosecrans as well. If so, “General (Joseph) Johnston (in Mississippi) should be moving either to Bragg or General Rosecrans’ lines.”
Lee next received a report from Brigadier General John D. Imboden, which he also forwarded to Davis: “General Imboden reports that 400 of his cavalry returned yesterday from an expedition north of Winchester. They report the railroad too strongly guarded to attack. He reports every bridge in Hampshire with a stronger guard than he can attack successfully.”
This “stronger guard” on the railroad indicated that Gilmore’s report was true–XI and XII corps were indeed moving west to reinforce Rosecrans. If so, Meade would indeed be weakened and possibly vulnerable to attack. Lee began planning to take the offensive. He hoped to drive Meade back to the Potomac for the winter, which would save northern Virginia from ravaging Federals and give Lee room to maneuver outside Richmond when the spring campaign began.
CivilWarDailyGazette.com; Freeman, Douglas Southall, Lee (Scribner, Kindle Edition, 2008), Loc 6393