Even though the Union forces outnumbered the Confederates by almost 2 to 1, Lee boldly went over to the offensive in the riskiest operation of his career. It paid off. On May 2, Stonewall Jackson led 28,000 men on a stealthy march through the woods to attack the Union right flank late in the afternoon. Owing to the negligence of the Union commanders, the surprise was complete. Jackson's assault crumpled the Union flank as the sun dipped below the horizon. Jackson then rode out to scout the terrain for a moonlight attack but was wounded on his return by jittery Confederates who mistook him and his staff for Union cavalry. Nevertheless, Lee resumed the attack next day. In three more days of fighting that brought 12,800 Confederate and 16,800 Union casualties (the largest number for a single battle in the war so far), Lee drove the Union troops back across the Rappahannock. It was a brilliant victory.