Ulysses S. Grant was given command of federal forces in southern Illinois and southeastern Missouri on August 21, 1861.
The Union Army of the Cumberland begins the Chickamauga Campaign on August 29, 1863. Federal forces headed east for passes in Lookout Mountain, near the intersection of Georgia, Alabama, and Tennessee.
On September 9, 1862, Confederate General Robert E. Lee writes Special Order No. 191. The order outlines the plans to divide his army: General Stonewall Jackson would go to Harpers Ferry, Virginia; General James Longstreet would head north to Boonsboro, Maryland; and the main portion of Lee's army would march to Hagerstown, Maryland. Copies of the order were made for each of Lee's commanders. One copy was either discarded or accidentally dropped on the ground. They were found four days later by a Union private and they were eventually given to Major General George McClellan, the commander of the Army of the Potomoc.
The first naval action of the Civil War occurred on September 13, 1861. Union Lieutenant John Henry Russell entered the Confederate controlled Pensacola Harbor and destroys the privateer, 'Judah'.