McClellan Moves Overland?

[OldReliable1862]

On January 27, 1862, President Lincoln ordered all Union army commanders to begin offensive operations by February 22, Washington's birthday. Four days later, he ordered McClellan to move overland to strike Joseph E. Johnston's army at Manassas and Centerville. McClellan objected stridently to this, and instead offered his own plan to land the Army of the Potomac at Urbanna, in the rear of Johnston's army. Lincoln eventually approved the plan after the March 8 council of war with McClellan's generals, though he did so reluctantly.

However, what if Lincoln had decided to stick to his guns and insisted that McClellan move overland? Historically, a decent chunk of McClellan's army was left behind to protect the capital, but how would events proceed if McClellan is able to attack with all of his forces?

 

[RedRover]

James Ford Rhodes opined a few decades later that McClellan's failure to abide the President's initial attack order might have been an error...

Gen. Johnston didn't know McClellan wasn't coming for him directly, and in early March completed his own retreat behind the Rappahannock, in which a vast store of quartermaster, commissary and ordnance supplies was abandoned or destroyed about Manassas etc. Johnston later noted that on February 22 (the original day set by Lincoln for an advance by McClellan), he had discussion with Jefferson Davis about the four likely routes of attack... the one he feared most being one by way of Fredericksburg...

 

[Saphroneth]

So the basic issue with an overland movement is that the Confederates can refuse battle (by retiring) unless you can either cut them off from Richmond (forcing them to break out) or threaten Richmond itself. Consequently, each line of defence that you have to overcome is an avenue for them to present you with a battle they want to take.


Going directly down the Orange and Alexandria, this means fighting for Manassass/Centreville and the line of the Bull Run, then the line of the Broad Run (potentially), then the line of the Cedar Run, then the line of the Rappahannock. Once all four of those lines have been overcome, you're where Grant's Overland started - and that one required Lee to be out of position and more than twice Lee's total numbers, while Johnston (when he defended the line of the Rapidan) was not out of position in the way that Lee was.


In addition, Grant's Overland logistically required the York river to be open for Union supplies - that's how Grant got around Lee's blocking positions that Grant could not overcome frontally. But without the Peninsular campaign, the York isn't open; the North Anna position is a blocker that can't be overcome by manoeuvre.



Johnston here is suggesting specifically that McClellan's army would march south to near Fredericksburg, but that it would do so in Maryland, and then cross the Potomac by shipping before moving to cross the Rappahannock at Fredericksburg. I think he might here be underrating the difficulty of moving a large force quickly across a river by shipping - it's doable, if you have enough ships, but the loading and unloading consumes quite a lot of time. About two thirds of Grant's post-Cold-Harbor army crossed the James by steamer and that took about three days by my understanding, which is about two of McClellan's 1862 divisions per day. Even if three divisions can be moved per day, that's still four days to move the whole field army, and so it's at least a few days before McClellan can apply his superior strength to Fredericksburg - which is, well, Fredericksburg and thus a strong position. All Smith (IIRC it was Smith in command there) would need to do would be to wreck the bridges as the Union army approaches, and that's days of delay for Johnston to reunite his forces - though it would certainly turn Johnston out of northern Virginia.


So the Fredericksburg route avoids multiple direct attacks on Confederate positions north of the Rappahannock, but it doesn't solve the really hard bit of the campaign, which is the overland south of the Rapidan. The Rapidan and the lower Rappahannock are a really logistically strong position, mostly because of the Wilderness.