A two-day American Civil War battle (April 6th and 7th, 1862) near Pittsburg Landing, Tennessee. Named for a Methodist chapel near the battlefield, this large engagement did much to determine the course of future battles in the western theatre.
The Union army, led by Major General Ulysses Simpson Grant, was massing for an attack on the Confederate held rail hub of Corinth, Mississippi. Feeling that the war was already as good as won, the Union commanders had not intrenched or otherwise made defensible their positions near the landing, preferring instead to drill and wait for the Army of the Ohio under major general Don Carlos Buell to link up before the assault. Unknown to them, however, the Confederate commanders had brought their own forces up to assault the Union positions, intending to smash Grant's army before Buell's could arrive.
Logistical difficulties and mass confusion reigned as units impeded each other on the march, and the Confederates arrived south of the Union positions several days behind the original plan. Nonetheless, they drew up to the Union positions on April 5th undetected. The men slept under arms overnight, and launched a surprise assault at dawn. The Union divisions, caught unprepared, were initially thrown back in disarray. By mid-morning they had settled into various secondary positions, most notable the division under Benjamin Prentiss which had taken what cover they could in a worn-down wagon trail. Several waves of Confederate troops failed to dislodge them. "It's a hornet's nest in there!" Johnny Reb cried. The crucible of the first day's battle was thus named.
Finally by 3:30pm, repeated mass assaults having failed, the Confederate command lined up over 60 guns facing the Hornet's Nest, loaded with canister shot and grape shot. The divisions covering Prentiss' flanks were broken, and Prentiss' troops were surrounded. He held out until 5:30pm when he was finally forced to surrender.
By the time Prentiss' men were taken, the Confederate army was exhausted. Their commander Albert Sidney Johnson had been killed while rallying his troops. Command passed to Confederate general Pierre Gustave Toutant Beauregard, who tried to move his troops on to force the Union to retreat, but they were spent. Twilight came on and ended the first day of battle.
Prentiss' stand had saved the Union from total defeat. Overnight Buell's men arrived, fresh and ready to stiffen the Union lines. The second day brought a reverse of the first, as Grant's fresh forces forced back Beauregard's exhausted ones, and the gains of the previous day were given up. The Confederates retreated to Corinth, leaving the field again to the Union.
Casualties were over 10,000 per side. The Confederates fell back without fulfilling their goal of smashing the Union army, and preventing Buell's linkup with Grant. The Union forces would ultimately follow them to Corinth. This in turn began a retreat and roll up of Southern forces that cost the CSA two states.
Shiloh National Military Park commemorates the site today.
Sources include Shelby Foote's The CIvil War, A Narrative, Volume One.