 Garfield 's promotion gave him command of the 20th Brigade of the Army of the Ohio , which was ordered in early 1862 to join Major General Ulysses S. Grant 's forces as they advanced on Corinth , Mississippi . Before the 20th Brigade arrived , however , Confederate forces under General Albert Sidney Johnston surprised Grant 's men in their camps , driving them back . Garfield 's troops got word of the battle and advanced quickly , joining the rest of the army on the second day to drive the Confederates back across the field and into retreat . The action , later known as the Battle of Shiloh , was the bloodiest of the war to date ; Garfield was exposed to fire for much of the day , but emerged uninjured . Major General Henry W. Halleck , Grant 's superior , took charge of the combined armies and advanced ponderously toward Corinth ; when they arrived , the Confederates had fled . 
