On this day in 1862, five days into his first invasion of the North, Gen. Robert E. Lee wrote Special Order No. 191 detailing how he wished to split his forces and the objectives he had set for each of those commands. Four days later, a lost copy of the order was discovered by an Indiana volunteer in the Army of the Potomac named Corporal Barton W. Mitchell. Within hours the captured order was in the hands of the commander of that army, Union General George McClellan.
The Union capture of Special Order 191 is one of the great "what ifs" of American history. A reasonable case can be made that without the order McClellan would have continued to dilly-dally and Lee would have confronted him in a place and time that better suited his army. That very well might have ended in Confederate victory and completely changed the outlook of the war, if not ended it then and there in favor of the CSA.
It's interesting stuff to speculate about over a beer, but that's about it for me. What happened next was historic enough. Four days after the order landed in his hands, McClellan would confront Lee's Army of Northern Virginia just outside the town of Sharpsburg, Maryland.