On a message board recently several people, including Eric Wittenberg, have insisted AP Hill made a flank attack against 9th Corps. This is understandable, even Harsh's Taken at the Flood says he did.
He didn't.
The descriptions in the OR don't match the events described in most books. I suspect it derives ultimately from Bruce Catton since whenever I've found an unsupportable myth in ACW history it usually started there.
All data is derived from the after action reports online at
www.aotw.org.
First that actually happened is this. AP Hill crossed his division at Boteler's Ford 3 miles in the Confederate rear, moved down the Saw Mill Road and ployed at the junction of the Harper's Ferry Road.
At the time Rodman was attacking NEE towards Sharpsburg. A break had occurred in his division, in Harland's brigade. The 8th CT attacked in the right direction, but the 16th CT moved down a slope and lost contact (carrying the 4th RI with it). They enter the Otto Cornfield and it is here they encounter AP Hill's lead brigade, Gregg's. According to the orders issued these two Union regiments should have been closed up to the 8th CT 500m to the NEE. As they advance east (further widening the gap with their parent brigade) they are encounter Gregg's brigade advancing in the reciprocal direction. The Confederates charge frontally and drive the two Union regiments back in disorder.
Rodman has received warning of AP Hill's movement "Look out welll on the left! The enemy are moving a strong force in your direction", and had ordered the 16th CT and 4th RI to close up and refuse Fairchild's flank. Harland, the Brigade Colonel comes back from the 8th CT to find them facing the wrong way and orders them to wheel round and attack the Confederates to the west (Toomb's brigade). As they are advancing they run straight into Gregg's brigade coming the other way.
Lt-Col Curtis of the 4th RI states he was flanked by a brigade of infantry advancing in 3 lines firing over each other. The only unit anywhere near the 4th RI which could have advanced was the 1st SC Rifles, who confirm it was them.
What seems to have happened is this:
1. 16th CT (maybe 700 bayonets, probably less) advances to contact with both 12th and 1st SC (about 400 bayonets between them). It overlaps the Confederate flank on the Confederate left, leading to concern about a flank move (which never happens).
2. There is a firefight.
3. 12th SC charges and breaks the right wing of the 16th CT. 4th RI moves to flank the 1st SC.
4. 12th SC is disordered and withdraws back to rally. 4th RI flanks the 1st SC.
5. 1st SC Rifles (maybe 200 bayonets) advances forward into the open flank the 4th RI have opened up.
6. The Union line crumbles and is routed.
While there is indeed a flank attack by the Confederates it was not deliberate. The 4th RI opened a flank and the 1st SCR took it, advancing roughly to their front.
Meanwhile Fairchild's brigade is doing well. They've driven back Drayton's and Kemper's brigades; "Arriving near a stone fence, the enemy - a brigade composed of South Carolina and Georgia regiments - opened on us with musketry. After returning their fire, I immediately ordered a charge, which the whole brigade gallantly responded to, moving with alacrity and steadiness. Arriving at the fence, behind which the enemy were awaiting us, receiving their fire, losing large numbers of our men, we charged over the fence, dislodging them and driving them from their position down the hill toward the village.... We continued to purse the enemy down the hill." (Fairchild's Report on the Battle).
However, his left flank is in the air. The 8th CT misses him, goes past and engages in a fight with Kemper's brigade on it's own! This isn't as stupid as it first sounds as the 8th CT is about the same strength as Kemper. When Fairchild withdraws, they didn't and basically were flanked on both sides and broken, losing more than half the regiment.
Fairchild states " It was then discovered that the enemy were moving up from the corn-field on our left to flank us, and I ordered the brigade to retire about 250 yards to the rear of the position we now held", however the Cornfield was 500m away. Thus it was at the Otto Cornfield the action was lost. Fairchild dodged a possible flank attack, but one that developed by a frontal assault on the 16th CT and 4th RI as the "break in". The Union force was never turned or flanked, the extreme left wing crumbled leading to the rest pulling back to compensate.
The action isn't over. Archer and Toombs(-) will make a frontal assault on Scammon's brigade as the Kanawha division attempts to repeat Rodman's attack, and will drive it back. However at least the Kanawha division gave the broken remnants of the 8th CT somewhere to run to, preventing the regiment being utterly lost.
9th Corps doesn't try again after this. Of their 8 brigades three (Ferrero's, Fairchild's and Harland's) have ceased to exist as meaningful units for the time, Scammon's (under Ewing) is disordered and has taken heavy casualties, as have Christ's, Nagle's and Moor's (although earlier, they've recovered order). Only Welsh's brigade is relatively fresh with about 1,000 bayonets available for the attack. Hence the doubt that 9th Corps could even hold their position if attacked.
On a minor related note, it's been suggested that McClellan should have cavalry piqueting the Harper's Ferry Road to block Hill. There are several problems with this. First, Hill didn't come up the Harper's Ferry Road. Second, the whole of Munford's cavalry brigade was piqueting it themselves. Thirdly, it's on the wrong side of the Antietam! If you could get cavalry there then the entire battlespace would be altered, but you couldn't.
