Antietam: McClellan's Pursuit of Lee (Answers)
1. The Army of the Potomac reached Frederick, Maryland, on
September 13. There, Union soldiers discovered a mislaid copy of the detailed
campaign plans of Lee's army [Special Order 191] wrapped around three cigars.
The order indicated that Lee had divided his army and dispersed portions
geographically, thus making each subject to isolation and defeat in detail.
McClellan waited 18 hours before deciding to take advantage of this
intelligence. His delay squandered the opportunity to destroy Lee's army.
2. On the night of September 13, the Army of the Potomac
moved toward South Mountain, with 2. 2. Maj. Gen. Ambrose Burnside's wing of the
army (the I Corps and IX Corps) directed to Turner's Gap
3. Maj. Gen. William B. Franklin's (V Corps and Maj. Gen.
Darius N. Couch's division of the IV Corps) to Crampton's Gap.
4. South Mountain is the name given to the continuation of
the Blue Ridge Mountains after they enter Maryland. It is a natural obstacle
that separates the Shenandoah Valley and Cumberland Valley from the eastern part
of Maryland. Crossing the passes of South Mountain was the only way to reach
5. Lee, seeing McClellan's uncharacteristic aggressive
actions, and learning through a Confederate sympathizer that his order had been
compromised, quickly moved to concentrate his army.
6. He chose not to abandon his invasion and return to
Virginia yet, because Jackson had not completed the capture of Harpers Ferry.
Instead, he chose to make a stand at Sharpsburg, Maryland.
7. In the meantime, elements of the Army of Northern
Virginia waited in defense of the passes of South Mountain.