General Joseph Hooker replaced Burnside as the commander of the Army of the Potomac. Hooker planned to keep Lee's concentration at Fredericksburg while he sent another force around the town to attack the Confederate flank. The movement began on April 27 and seemed about to succeed. But Hooker hesitated, and on April 30 withdrew his flanking force to a defensive positio at Chancellorsville. On May 1, Lee left a small position at Fredericksburg and boldly moved to attack Hooker. He dispatched Stonewall Jackson to attack Hooker's right while he struck in front. The attack, on May 2, cut the Northern Army almost in two, but Union troops managed to set up a defensive line. Hooker retreated four days later on May 6. The Confederate victory cost the life of General Thomas Jackson, who was shot accidentally by his own men. His left arm had to be amputated, and Lee told Jackson's chaplain: "...He lost his left arm, but I have lost my right arm." Jackson, wounded on May 2, died May 10, eight days later from pneumonia and the effects of the amputation.