On October 8, 1862, the largest Civil War battle in Kentucky began in the village of Perryville as thirsty armies converged on the last stagnant pools of Doctors Creek during a severe drought. The episode explains why Lincoln considered Kentucky essential, how the state’s declared neutrality collapsed by September 1861, and how the divided Confederate command of Braxton Bragg and Edmund Kirby Smith produced a disorganized invasion while Don Carlos Buell raced to protect Louisville.

The battle itself was shaped by strange conditions: a temperature inversion created an acoustic shadow that kept Buell, injured from a fall from his horse and two miles away, from hearing the fighting. Bragg attacked with about 16,000 men believing he faced a small detachment, when Buell actually had around 55,000. Raw Union recruits were swept off the Open Knob, fighting spilled into 10 to 12 foot cornfields, and Leonidas Polk bluffed his way out of a Union regiment after riding into it by mistake. Bragg won the field but lost the campaign, retreating to Tennessee and leaving Kentucky in Union hands.

• Bragg left his army to attend the inauguration of a Confederate governor in Frankfort, which was interrupted by Union cannon fire.
• Scientists link the drought to the eruption of an African volcano the year before, which may have disrupted the jet stream.
• Patrick Cleburne’s men, wearing captured blue pants, were shelled by their own artillery, and Cleburne was wounded in the ankle.
• A burning log barn on Squire Henry Bottom’s farm killed wounded Union soldiers who had crawled inside for shelter.
• Polk’s volley into the 22nd Indiana caused 65 percent casualties, and two days after the battle the drought broke with heavy rain.