On April 27, 1863, the Army of the Potomac marched North towards the Rappahannock River and Rapidan ford. Within three days, they had 70,000 Federals to face the flank of General Lee. Lee, however, caught on to the scheme of General Joseph B. Hooker in time to counter it. He left 10,000 troops at Fredericksburg and sent 45,000 men towards Chancellorsville. The Union defeated the Confederates by attacking the Confederate flanks. This is where General "Stonewall" was wounded in the left arm and right hand, necessitating the amputation of his arm. Afterwards, he died of pneumonia.