Special Order 191

Special Order 191 (series 1862), also known as the "Lost Dispatch" and the "Lost Order", was a general movement order issued by Confederate Army General Robert E. Lee in September 1862, during the Maryland Campaign of the American Civil War. A discarded copy of this order was recovered several days later by Union Army troops in Frederick County, Maryland; it was passed to General George B. McClellan, who subsequently altered his own forces' movement and defeated Lee at the Battle of Antietam. Historians differ on how much the discovery contributed to McClellan's victory.