When Grant captured Fort Donelson in February 1862, the obvious next step was to advance against the important rail center of Corinth, Mississippi. C F. Smith, superseding Grant, began to build up a base at Pittsburg Landing on the Tennessee River. On March 17, Grant resumed command and continued to augment his forces. By late March he was awaiting only Don Carlos Buell's 20,000 men before commencing operations.
Meanwhile, the Confederates reorganized at Corinth under Albert Sidney Johnston, with P. G. T. Beauregard second in command. To surprise Grant before Buell could join him, Johnston marched his army of 40,000 on April 3, but his inexperienced troops took three days to cover the twenty-five miles to Pittsburg landing. What was worse, they moved in a continual uproar, shouting and firing off guns. Beauregard, sure that Grant was alerted, advised calling off the attack. Incredibly, the Federal were not prepared; they were not even entrenched. They were camped with the river to the east and two marshy creeks north and west. Johnston planned a three-pronged attack; the strongest drive to be on the right to wedge the Federals away from the river and the support of their gunboats, and force them into the swamps along the creeks.
Johnston's morning attack on the 6th drove the Federals back in wild confusion. Grant, hurrying to the scene from his headquarters downriver, found his men in slow retreat all along the line except where Prentiss' division was holding an almost isolated position, the famous Hornets' Nest. But midafternoon disorganization had slowed the Confederate assault. Johnston was killed directing the all-important east flank attack, and Beauregard suspended operation at dusk.
Buell arrived during the night. Next morning at 7:30 Grant attacked, retaking most of the ground lost on the 6th. Then the Confederates rallied and heavy fighting swirled for a time around Shiloh Church. But when Beauregard learned that he could not expect reinforcements, he ordered withdrawal, and retired almost unmolested.
One of the bloodiest battles in the West, fought for the most part by green troops, Shiloh shocked and sobered both North and South. But the Union victory foreshadowed the eventual splitting of the Confederacy along the Mississippi.