In early 1863 Joseph Hooker took over a demoralized Army of the Potomac after Fredericksburg, fixed its supply and hospital systems, introduced furloughs, and created the Bureau of Military Information under George H. Sharpe, which used spies, signal stations and telegraph-equipped balloons. His plan sent cavalry to cut Lee’s railroad, left a force at Fredericksburg, and marched more than 70,000 men across the Rappahannock and Rapidan rivers to Chancellorsville. His army of about 134,000 faced a Confederate force of barely 60,000.

Lee split his army, then split it again, sending Stonewall Jackson with about 28,000 men on a 12-mile march around Hooker’s open right flank. Warnings from pickets and Captain Hubert Dilger were dismissed by Oliver O. Howard, and at 5:30 p.m. Jackson’s men routed the 11th Corps. That night Jackson was shot by the 18th North Carolina and died of pneumonia a week later. Hooker, concussed when a cannonball split a pillar of the Chancellor house, kept command and withdrew on May 6, with about 17,000 Union and 13,000 Confederate casualties.

• Hooker pulled his troops off open ground into the Wilderness, dense second growth left by clear-cutting for iron furnaces.
• The largely German 11th Corps, many of them refugees of the 1848 revolutions, faced distrust at headquarters.
• Deer, foxes and rabbits burst out of the woods just ahead of Jackson’s attack.
• Jeb Stuart took over Jackson’s infantry command, and Confederate guns at Hazel Grove shelled the Union center.
• Lee turned part of his army east to stop John Sedgwick’s advance at Salem Church.