THE GETTYSBURG CAMPAIGN, 1863. - After the defeat at Fredericksburg, Burnside was removed, and General Hooker put in command of the Army of the Potomac. "Fighting Joe," as Hooker was called, led his army of 130,000 men against Lee and Jackson, and after a stubborn fight at Chancellorsville (May 1-4, 1863) was beaten and fell back. [1] In June Lee once more took the offensive, rushed down the Shenandoah valley to the Potomac River, crossed Maryland, and entered Pennsylvania with the Army of the Potomac in hot pursuit.