With artillery projectiles flying in every direction, Union Gen. George G. Meade galloped through the fields, encouraged his men, and looked for an opportunity to attack. When Union artillery blew up two Confederate ammunition chests, Meade took the initiative and ordered his men to charge. His division surged toward Prospect Hill, where Confederate forces waited. Meade's troops advanced directly into a 600-yard gap in the Confederate line left unmanned because the swampy ground was mistakenly deemed impassible. Union troops pushed through the swampy woods, wrecked two Confederate brigades, and expanded the size of the gap in the Southern line. Both sides became disorganized and scrambled to regroup. Meade needed reinforcements, and when Gen. David Birney failed to advance in support, Meade rode to the rear and berated him until Birney hastily organized his division and pushed forward, but it was too little, too late. Out of ammunition and out of time, Meade's men found it impossible to hold on, and Confederate Gen. Maxcy Gregg, struck in the spine during the fighting, died two days later.