Just before 5:00 am the explosion blew up a Confederate artillery battery and most of an infantry regiment. The blast killed at least 278 Confederates instantly. The crater caused by the explosion was more than long, across and deep. Following the explosion, the untrained Union troops were slow to leave their trenches. Instead of avoiding the crater they ran right into it. The walls of the crater exposed red clay making them too slippery to climb out of. The Confederates recovered quickly and began firing down directly on the Union troops who were unprotected. To try to save the situation, after four hours of fighting Burnside ordered the black troops to attack. At this point they could only follow the white soldiers into the crater. They had to force their way past the dead, wounded and demoralized white troops to get into the fight. As more Confederates joined in, they set up a tremendous crossfire into the crater. Mortar shells were dropped on the Union troops and the Confederate cannons were rolled up to the edge and fired canister shot at the soldiers trapped in the crater. The situation quickly turned from a one-sided battle into a race riot. As Union soldiers surrendered, black soldiers were given no quarter. Those who were allowed to surrender were murdered by Confederate troops as they were marched to the rear. Some Confederates later expressed regret that they could not kill them fast enough, as a few black troops made it to the rear alive.