Tactics and Weapons at Antietam
Civil War infantry fought in double-ranked line of battle, standing shoulder to shoulder, to mass fire to the front or rear. This formation was vulnerable on the flanks. "Bull" Sumner's command was torn up in the "West Woods Massacre" because Jackson's Confederates hit him on front and flank at the same time.
The linear tactics of the infantry were designed around the muzzle-loading smoothbore flintlock musket firing a round lead ball. It had an effective range of only 70 to 100 yards and misfired one time in six, making the bayonet a very important piece of equipment. During the American Revolution, the Napoleonic Wars, and the Mexican War, only specialist troops had rifles, which were much slower to load than a smoothbore.
With the perfection of the Minie bullet in the decade prior to the Civil War, the common soldier now carried a percussion or cap-lock rifle. A man-sized target could now be hit consistently at 300 yards. Many Civil War generals piled up thousands of dead soldiers to learn the lesson that frontal assaults against an entrenched enemy armed with rifles were no longer practical. The rifle had made the defense stronger than the offense. Battle lines were now rarely able to close and decide the issue at "point of bayonet," as was done before the common use of the rifle.
The artillery was also in transition, going from smoothbore to rifle, from bronze or iron to steel. Civil War field artillery was all direct fire. Maximum effective range was 1,500 to 1,900 yards, or about a mile. Much of the artillery action at Antietam was at half this range, so artillery was very deadly. Malvern Hill, Antietam, and Gettysburg in the east, and Stones River in the west rank as some of the most significant field artillery battles of the Civil War.
The cavalry at Antietam was employed well by the Confederates and poorly by the Federals. J.E.B. Stuart's troopers screened the Army of Northern Virginia and kept McClellan from gaining accurate information about Confederate numbers and deployment. The Confederate cavalry tied in the army's flanks to the Potomac River. Being grouped in mass and practiced at maneuvering in large formations, they were able to develop combat power quickly.
On the other hand, a large fraction of the Federal cavalry was frittered away in penny packets as guards and messengers at division and corps headquarters. Had the U.S. cavalry been properly deployed on the flanks, they could have detected A. P. Hill's arrival and broken up or delayed his attack. Thus, Sharpsburg could have been carried and Lee decisively beaten with his route of retreat cut off. The failure of the Union cavalry at Antietam is not due to any lack of gallantry or good equipment, but rather to poor central direction by a defensive-minded commanding general.--Paul Chiles