On the morning of April 6, 1862, 40,000 Confederate soldiers under the command of Gen. Albert Sidney Johnston poured out of the nearby woods and struck a line of Union soldiers occupying ground near Pittsburg Landing on the Tennessee River. The overpowering Confederate offensive drove the unprepared Federal forces from their camps and threatened to overwhelm Ulysses S. Grant’s entire command. Some Federals made determined stands and by afternoon, they had established a battle line at the sunken road, known as the “Hornet's Nest.” Repeated Rebel attacks failed to carry the Hornet's Nest, but massed artillery helped to turn the tide as Confederates surrounded the Union troops and captured, killed, or wounded most. During the first day’s attacks, Gen. Johnston was mortally wounded and was replaced by P.G.T. Beauregard. Fighting continued until after dark, but the Federals held. By the next morning, the reinforced Federal army numbered about 40,000, outnumbering Beauregard’s army of less than 30,000. Grant’s April 7th counteroffensive overpowered the weakened Confederate forces and Beauregard’s army retired from the field. The two day battle at Shiloh produced more than 23,000 casualties and was the bloodiest battle in American history at its time.