History Learner
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In the weeks following the conclusion of the Seven Days, it became clear to the Confederates that McClellan was no longer a threat to Richmond and was preparing to withdraw altogether. Content the Army of the Potomac was no longer an active concern, Robert E. Lee's attention thus shift to John Pope's 50,000 strong Army of Virginia advancing south overland. Lee, with his Army of Northern Virginia also at around 50,000 strong, soon marched to face Pope and thus engendered the Northern Virginia Campaign. Initial major clashes would be held at Cedar Mountain, ending in a close run Confederate victory that forced Pope to withdraw to just above the Rapidan River.
Pope's new position, however, was dangerously exposed. The aforementioned Rapidan was directly in front of his forces while the Rappahannock River was to his right, effectively meaning his forces were in a triangle and could be boxed in. Worse, Cedar Mountain could screen a movement of Confederate forces to cross the Rapidan and slam into the exposed left flank of Pope and then pin Pope's Army between the two rivers. Further, prior to the start of the attack, Fitzhugh Lee’s cavalry was to burn the railroad bridge at Rappahannock Station, which would cut Pope’s only supply line. Without supplies and with no escape against a numerically equal Confederate force having collapsed his left flank, the annihilation of Pope's Army was imminent. It was at this point, however, that disaster struck for Lee. From the Osprey Campaign Series, Second Manassas 1862 (Pg 27):
The obvious PoD here is Fitz Lee does not take his detour which forced Lee to delay the attack as well as directly resulted in the capture of Major Fitz Hugh. Without this chain of events, General Lee's attack is able to proceed as planned, resulting in the destruction of Pope's army. Now, the destruction of an entire Federal force of 50,000 in of itself is pretty decisive as far as the war goes. IOTL the Anglo-French were prepared to intervene and nearly did so over the historical Second Battle of Manassas despite that being far less decisive than this "Battle of the Rapidan". Still, it's going to take some time for London and Paris to learn exactly what has happened and then get communications back across the Atlantic. This means there's still going to be some fighting to occur before the Anglo-French fully involve themselves.
Going into the Alt-Maryland Campaign, the first thing to be noticed is that McClellan's Army of the Potomac is going to be massively under-strength:
The First and Second Corps were with Pope's Army, and their removal means McClellan is short 33,669 men. Subtracted from his overall strength, that means the Army of the Potomac will only have 53,495 troops to face Lee and this is assuming Halleck doesn't force him to detach more to bolster the defenses of Washington. As for Lee, historically in the aftermath of Second Manassas his strength was approaching 75,000 according to John Owen Allen's “The Strength of the Union and Confederate Forces At Second Manassas” (Masters Thesis, George Mason University, 1993). Here's a link to where you can review the excel spreadsheet they have outlining this strength.
Due to straggling, Lee was ultimately whittled down to somewhere between 40,000 to 50,000 by the time of IOTL Antietam, but here this can largely be avoided thanks to the early end of the Northern Virginia campaign. IOTL fighting in said campaign didn't conclude until the start of September and was then immediately followed by Lee pushing into Maryland, resulting in his men being increasing exhausted from the continuous combat. In this ATL, however, combat operations are largely concluded by the 20th to 21st, meaning the bulk of Lee's forces will have several days to rest before ultimately pushing into the North to face a much weakened Army of the Potomac. Given this, I think it's safe to say Lee will win any engagement he gets into, probably directly before the Anglo-French intervention begins.
Pope's new position, however, was dangerously exposed. The aforementioned Rapidan was directly in front of his forces while the Rappahannock River was to his right, effectively meaning his forces were in a triangle and could be boxed in. Worse, Cedar Mountain could screen a movement of Confederate forces to cross the Rapidan and slam into the exposed left flank of Pope and then pin Pope's Army between the two rivers. Further, prior to the start of the attack, Fitzhugh Lee’s cavalry was to burn the railroad bridge at Rappahannock Station, which would cut Pope’s only supply line. Without supplies and with no escape against a numerically equal Confederate force having collapsed his left flank, the annihilation of Pope's Army was imminent. It was at this point, however, that disaster struck for Lee. From the Osprey Campaign Series, Second Manassas 1862 (Pg 27):
The obvious PoD here is Fitz Lee does not take his detour which forced Lee to delay the attack as well as directly resulted in the capture of Major Fitz Hugh. Without this chain of events, General Lee's attack is able to proceed as planned, resulting in the destruction of Pope's army. Now, the destruction of an entire Federal force of 50,000 in of itself is pretty decisive as far as the war goes. IOTL the Anglo-French were prepared to intervene and nearly did so over the historical Second Battle of Manassas despite that being far less decisive than this "Battle of the Rapidan". Still, it's going to take some time for London and Paris to learn exactly what has happened and then get communications back across the Atlantic. This means there's still going to be some fighting to occur before the Anglo-French fully involve themselves.
Going into the Alt-Maryland Campaign, the first thing to be noticed is that McClellan's Army of the Potomac is going to be massively under-strength:
The First and Second Corps were with Pope's Army, and their removal means McClellan is short 33,669 men. Subtracted from his overall strength, that means the Army of the Potomac will only have 53,495 troops to face Lee and this is assuming Halleck doesn't force him to detach more to bolster the defenses of Washington. As for Lee, historically in the aftermath of Second Manassas his strength was approaching 75,000 according to John Owen Allen's “The Strength of the Union and Confederate Forces At Second Manassas” (Masters Thesis, George Mason University, 1993). Here's a link to where you can review the excel spreadsheet they have outlining this strength.
Due to straggling, Lee was ultimately whittled down to somewhere between 40,000 to 50,000 by the time of IOTL Antietam, but here this can largely be avoided thanks to the early end of the Northern Virginia campaign. IOTL fighting in said campaign didn't conclude until the start of September and was then immediately followed by Lee pushing into Maryland, resulting in his men being increasing exhausted from the continuous combat. In this ATL, however, combat operations are largely concluded by the 20th to 21st, meaning the bulk of Lee's forces will have several days to rest before ultimately pushing into the North to face a much weakened Army of the Potomac. Given this, I think it's safe to say Lee will win any engagement he gets into, probably directly before the Anglo-French intervention begins.
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