The Union forces captured Confederate battle plans that provided crucial intelligence during the Battle of Antietam.

A copy of General Lee's Special Order No. 191 was discovered by Union soldiers, detailing the movements and positions of Confederate troops. This intelligence allowed Union commanders, particularly George McClellan, to better anticipate Lee's strategies and adjust their own plans accordingly. The capture of these orders significantly impacted the battle, providing the Union with a strategic advantage that informed their movements and decisions throughout the engagement, although McClellan's execution of this advantage remained cautious.