Once, in midwinter, the armies became active when Burnside attempted to move his army and cross the river above Fredericksburg; but only for a few days, for that unfortunate General's plans were ruined by a deluge and his army "stuck in the mud." General Hooker took his place. [Sidenote: _The Coming of Spring_] About April 26 Hooker's great army, "The finest army on the planet," he bombastically called it, moved up the river and began crossing. It was his purpose to get behind Lee's lines, surprise him and defeat him from the rear. On April twenty-ninth and thirtieth, Hooker got in position around Chancellorsville, in strong entrenchments, a part of his army amounting to 85,000 men, but the Confederate skirmishers were already in front of him. It was the Northern Commander's plan for Sedgwick, left at Fredericksburg with 40,000, to drive past Fredericksburg and on to Chancellorsville, and thus to place the Southern forces between the two big Federal armies and crush it. [Sidenote: _The First Aerial Scout_] Before the great battle of Chancellorsville began, this message came down from the first balloon ever successfully used in war, tugging at its cable two thousand feet above the Scott house, on Falmouth Heights: Balloon in the Air, April 29, 1863. Major-General Butterfield, Chief of Staff, Army of the Potomac. General: The enemy's line of battle is formed in the edge of the woods, at the foot of the heights, from opposite Fredericksburg to some distance to the left of our lower crossing. Their line appears quite thin, compared with our forces. Their tents all remain as heretofore, as far as I can see. T. C. S. LOWE, Chief of Aeronauts. But the force did not "remain as heretofore" long, though the tents were left to confuse the enemy, for on April 29 General Anderson moved to Chancellorsville, followed on April 30 by General McLaws; and under cover of darkness "Stonewall Jackson" moved to the same place that night, with 26,000 men. On May 1, then, Hooker's 91,000 at Chancellorsville were being pressed by Lee's army of 46,000. General Early's command of 9,000 and Barksdale's brigade of 1,000 and some detached troops were left to defend Fredericksburg against Sedgwick's corps, which was now crossing the Rappahannock, 30,000 strong. At 11 A. M., May 1, General Lee's army, with Jackson's corps on his left, began the attack at Chancellorsville, of which this dispatch speaks: Balloon in the Air, May 1, 1863. Major-General Sedgwick, Commanding Left Wing, Army of the Potomac. General: In a northwest direction, about twelve miles, an engagement is going on. T. C. S. LOWE, Chief of Aeronauts. [Sidenote: _Fight at Chancellorsville_]