A copy of General Robert E. Lee's battle plans was found by Union soldiers in a field outside Frederick, Maryland, providing an unexpected strategic advantage prior to the imminent confrontation at Antietam. The documents included instructions detailing Confederate troop movements and engagement strategies, specifically revealing the intentions of the Confederate Army as it maneuvered into Maryland. In the context of the ongoing Civil War, this discovery was crucial both for intelligence gathering and for morale among Union forces. Antietam was poised to be a significant engagement, and the leaked information would greatly shape tactical preparations for the Union Army.

The significance of this find lay in the advantage it provided Union commanders, particularly Major General George B. McClellan. He was able to anticipate Lee's strategy and possibly alter his own plans to achieve a better outcome during the upcoming battle. The Union soldiers' discovery underscored the role of intelligence in military strategy, as the possession of Lee's orders meant that the Union could formulate an optimal response to Confederate movements. As the preparations for the Battle of Antietam unfolded, the implications of this intelligence would reverberate throughout the entirety of the conflict.

As the battle commenced shortly after this discovery, the Union's prior knowledge of Confederate plans played a critical role in the engagement's dynamics. While McClellan's forces were eventually unable to capitalize fully on the intelligence at hand, the event emphasized the ongoing fight for control over information within the war. Thus, the recovery of these battle plans became a notable instance of how intelligence can influence military outcomes in wartime, shaping future strategies for both the Union and the Confederacy.