In going through Timothy Reese's wonderfully dense and rich new book, High-Water Mark: The 1862 Maryland Campaign in Strategic Perspective, we reached the point in Reese's dissection of the Maryland Campaign where he analyzes McClellan's famous Sept. 13 order to General William Franklin.
I would like to present just a few key passages from his fourth chapter. My ambitious exercise in minimalism ridiculously truncates his material to blog-size with at least one benefit, that you hear Reese's own voice directly on this important matter.
Though well acquainted with McClellan's 6:20 P.M. dispatch to Franklin, historians have habitually cited it out of legitimate context irrespective of a highly mobile strategic situation, its sense lost in the shuffle.
McClellan's grand design was flawless in that it required Franklin to isolate McLaws, guardian of Harpers Ferry's backdoor, his being the only Confederate force north of the Potomac which could conceivably hinder any move against Longstreet at Boonsboro or potentially impede Franklin's westward progress.
With or without constraint, McClellan then spelled out the ultimate objective he allotted to Sixth Corps. This single statement has been routinely misunderstood, misconstrued, or oversimplified by historians due to its extreme complexity and because its purpose ultimately failed.
... Franklin had to crush McLaws and presumably Anderson, before the [HF] garrison could be assimilated. Thereafter the pontoon bridge into Harpers Ferry could be sealed isolating Jackson, then Franklin's combined forces could march up Pleasant Valley to pressure Longstreet's flank, provided McClellan's assault on Turner's Gap was stopped dead in its tracks.
Conversely, should McClellan burst victoriously through Turner's Gap, Franklin would then be at large to push westward through "Rohrersville Pass" to Sharpsburg or even Williamsport, driving a substantial moving wedge between Longstreet and Jackson as the former retired. In doing so he would force Longstreet to either confront him, or further withdraw into western Maryland, seeking another ford by which to rejoin Jackson. By the same token, Jackson, whether Harpers Ferry fell to him or not, would be compelled to cross the Potomac at Shepherdstown for the same purpose, or likewise move upriver to reunite with Longstreet farther west near to Williamsport. Franklin's mobile wedge would simultaneously impose the same nerve-wracking alternatives on both halves of Lee's army without his necessarily committing to a set-piece battle, Lee all the while relentlessly pressed by the cumulative might of McClellan's main body.
In summary, Franklin was tasked with an aggressive three-way mandate, its first element being the seemingly non-negotiable relief of Harpers Ferry, followed by one of two options to be determined by the outcome at Turner's Gap - a corps offensive in Pleasant Valley to the south against McLaws then north to threaten or at least contain Longstreet, or west as a flying column to keep the Confederate army halved.
Theoretically, Franklin would reasonably construe his partitioning role as alternately directed toward both Jackson and Longstreet, provided he shadowed whichever command first showed an inclination to reunite with the other.
In any event, neutralization or immobilization of McLaws command would have been a mere theoretical exchange of minor chess pieces should Harpers Ferry be lost, the primary objective still well in view to the north.
... McClellan chose to accompany the main body of his army to Turner's Gap, clearly intent on confronting Lee personally beyond South Mountain in a textbook Napoleonic showdown. By assuming this formal, geographically polarized posture, he relinquished his master stroke to Franklin, his proxy, via extended written guidance, when arguably such a delicate, pivotal maneuver might have been better executed, or at least overseen, by the master.
More on High-Water Mark on Tuesday.