Sheridan was assigned to command the 11th Division, III Corps, in Maj. Gen. Don Carlos Buell's Army of the Ohio. On October 8, 1862, Sheridan led his division in the Battle of Perryville. Under orders from Buell and his corps commander, Maj. Gen. Charles Gilbert, Sheridan sent Col. Daniel McCook's brigade to secure a water supply for the army. McCook drove off the Confederates and secured water for the parched Union troops at Doctor's Creek. Gilbert ordered McCook not to advance any further and then rode to consult with Buell. Along the way, Gilbert ordered his cavalry to attack the Confederates in Dan McCook's front. Sheridan heard the gunfire and came to the front with another brigade. Although the cavalry failed to secure the heights in front of McCook, Sheridan's reinforcements drove off the Southerners. Gilbert returned and ordered Sheridan to return to McCook's original position. Sheridan's aggressiveness convinced the opposing Confederates under Maj. Gen. Leonidas Polk, that they should remain on the defensive. His troops repelled Confederate attacks later that day, but did not participate in the heaviest fighting of the day, which occurred on the Union left.