I've decided to share what I've got to so far in terms of viable march routes for closing up with the Rapidan.
In previous posts I have largely modelled from the point of view that Jackson would be able to move fairly soon after the point of divergence; that is, that a few days after Lee abandoned Culpeper Jackson would be able to begin moving to unite with Lee.
This has been a position used for modelling on the basis that it is one acceptable to (indeed raised by) those who think that Jackson's pause was incidental and not reflective of his true ability to move; the fact that the modelling has indicated that Lee would be in a difficult strategic situation anyway is a bonus.
In this case, however, I will be representing a more middle of the road position in terms of Jackson's ability to move, because I will be modelling march distances and corps positions for both sides. I will assume that Jackson cannot or does not begin moving until three days after Longstreet abandons Culpeper, or the 16th of November - whichever is soonest. Note that the 16th is still two days before Jackson historically began to move, and it is two days after Lee's order to Jackson which stated that (1) there was no rear for Jackson to raid and (2) that Jackson should unite with Longstreet "the sooner the better".
Effectively in this model Lee's letter of the 18th November was the trigger for Jackson to finally begin moving, and Jackson begun moving three days later (on the 21st) and a comparable letter would be sent when Longstreet abandoned Culpeper.
I will be assuming in addition that the marching speed of the Union is nine miles per day on average and that all Confederate formations march at ten miles per day. I will be assuming that all Union forces have full wagons as of the 10th, that they can top off to full wagons from any point along the Warrenton branch and that the line south to Culpeper/Rapidan/Orange can provide supplies sufficient for about one third of McClellan's army per day. (Full wagons here represents the ability to operate as a flying column for at least nine days.)
For the sake of simplicity I will treat McClellan's army as consisting of six corps of equal strength (1st, 2nd, 5th, 6th, 9th, 11th). 1st, 2nd and 5th start at Warrenton, 9th at Waterloo on the Rappahanock, 6th at New Baltimore and 11th at Greenwich; this is a simplification but represents the "centre of gravity" of the corps. It's a matter of just a few miles as to where exactly they start and this will largely "come out in the wash".
Each corps is 23,550 AP or 15,700 Effectives.
I will assume that Longstreet abandons Culpeper on the day McClellan's forces bivouaced within a day's march of the city (that is, he marches out promptly the next morning). I will also assume that a corps forms a road column about 5-6 miles long and thus that two corps can fit down a road in a day (by staggering their marches) but cannot follow one another closer than ca. 6 miles, and that where I do not have a better map all marked roads on the OR map are viable march routes but that no roads not marked are viable march routes. (An OR map showing NE Virginia specificially is sufficient to prove that this is an underestimate of the amount of viable march routes.)
Each corps will be assumed to start the day closed up and end the day closed up, each component having moved nine miles (for the Union). Ditto for CS divisions or commands but ten miles per day.
The first topic will be the approaches to Culpeper.
Planned routes of march:
9th Corps - Waterloo-Amissville-Rixey's Ford- Rixeyville - El Dorado Mill - reach the Griffinsburg-Culpeper road at the crossroads.
1st Corps - Warrenton-Waterloo-Amissville-Rixey's Ford- Rixeyville-Culpeper
2nd Corps - Warrenton-Sulphur Springs - Jefferson - Brandy Station - Culpeper
5th Corps - Warrenton - Liberty - Rappahanock Station - Kellysville - Stevensburg
6th Corps - New Baltimore - Warrenton - Liberty - Rappahanock Station - Brandy Station - Stevensburg
11th Corps - Greenwich - Warrenton Junction - Elkton - Kellysville
10th November.
9th Corps: Waterloo to Amissville (5.2 miles) and then to Corvin's Cross Roads (to turn left). The nine mile point is roughly at the schoolhouse on the route towards Rixey's Ford.
1st Corps: Warrenton to Waterloo along the contemporary route (now a back road) is 6.8 miles. 1st Corps is following 9th Corps at a distance of just under 7 miles, and encamps between Waterloo and Amissville (40% of the way to Amissville from Waterloo).
2nd Corps: Warrenton via Sulphur Springs (now Farquier Springs) to Jeffersonton is 9.5 miles. 2nd Corps encamps on the outskirts of Jeffersonton.
5th Corps: On the modern route via Opal (which seems to be the historical Fayetteville) - a route which goes right past "Liberty Drive" at about the right spot for the historical Liberty - it's 10.8 miles from Warrenton to Bealton Station itself. Reducing the distance down to 9 miles seems to be pretty much Liberty itself (meaning the junction). 5th Corps encamps at Liberty.
6th Corps: New Baltimore to Warrenton is about 7 miles (ignoring the modern roads and following a more contorted route). 6th Corps makes it about two miles out of Warrenton towards Liberty, and camps seven miles behind 5th.
11th Corps: The modern route from Greenwich to Calverton (the modern location of Warrenton Junction) is about nine miles. Based on the contemporary map this looks like it's pretty close to the historical route, so for simplicity I'll simply treat it as a single nine mile march.
11th November.
None of McClellan's forces are within ten miles of Culpeper yet; Longstreet stays put.
9th Corps: The march to Rixeyville is 4.6 miles and then 9th Corps continues via Eldorado Mill towards the Culpeper-Sperryville Pike. The total distance from the halt on the 10th to the junction that's the 9th Corps target is 13.3 miles, and 9th halts just south of Eldorado Mill.
1th Corps: Warrenton via Waterloo and Amissville to Rixeyville is 13.6 + 6.8 miles, and 1st Corps halts not far short of Rixey's Ford.
(n.b. the configuration here suggests 9th Corps may delay a bit or 1st Corps march harder so 9th Corps is not "dangled over the river" by itself. This could be made up for with harder marches or delays on the 12th.)
2nd Corps: 2nd Corps marches half a mile into Jeffersonton and turns south. Jeffersonton to Brandy Station via the modern routes is 11.7 miles (going through Alanthus) but this is a longer and less direct route than the one on the period map; the route on the period map appears nearly straight. The straight-line distance is 9.3 miles, so I will assume that the actual length of the route is such that 2nd Corps makes it over Welford's Ford and halts at the crossroads north of Brandy Station.
5th Corps: for simplicity 5th Corps will march to Bealton and then to Rappahanock, and from there towards Kellysville. It's 1.8 miles to Bealton (and a bit further to the station), and then 4.8 miles to Rappahanock Station; from there to Kelly's Ford is another 3.4 miles. 5th Corps encamps two miles short of Kelly's Ford.
6th Corps: follows behind 5th Corps and encamps at Bealton Station.
11th Corps: Warrenton Junction to Elkton is 9 miles, camps there.
12th November.
Longstreet abandons Culpeper, making for Rapidan and thence Gordonsville.
With a ten mile march he makes it to the area of Mitchell's Station.
This means that march orders need to be re-evaluated. The goal of the Union army is now closing up to the Rapidan and crossing it successfully.
Concept of operations:
9th Corps swings wide to Madison Court House (to push Walker back off Roberton's River) and then makes for Madison Mills (to cross the Rapidan).
1st and 2nd march through Culpeper. 1st then marches for Madison Mills (to cross the Rapidan as part of Burnside's Grand Division) and 2nd makes for the area of Rapidan itself.
5th aims for the fords downriver of Rapidan (Sommerville's Ford and Racoon Ford).
6th and 11th move on Germanna Ford to march straight from there to Fredericksburg.
Thus Burnside's GD crosses the Rapidan upstream of Rapidan Station and Porter's GD does so downstream of Rapidan Station.
Planned routes of march:
9th Corps - El Dorado Mill - reach the Griffinsburg-Culpeper road at the crossroads - James City - Madison Court House - Madison Mills.
1st Corps - Rixey's Ford- Rixeyville - Culpeper - Robertson's Ford - Madison Mills.
2nd Corps - Brandy Station - Culpeper - Mitchell's Station - Rapidan Station (north of river)
5th Corps - Kellysville - Stevensburg - Racoon Ford
6th Corps - Rappahanock Station - Brandy Station - Stevensburg - Germanna Ford
11th Corps - Elkton - Kellysville - Germanna Ford.
One odd result of this is that 6th and 5th Corps arguably march further than if their roles were reversed, but 2nd and 5th are operating as a single wing and 6th and 11th are operating as a single wing.
The likely result of this set of manoeuvres is that Longstreet will be compelled to withdraw from the line of the Rapidan and pull back at least to Orange if not to Gordonsville. Burnside's Grand Division will cut in behind him if he tries to hold Rapidan Station, while if he puts his main effort into resisting the advance from Madison Mills then it will be possible to attack him from the north.
(More detail will be given on this when we switch to the Orange County map.)
12th November continued:
9th Corps advances halfway from their halt point on the 11th to Madison Court House. (It's 18.5 miles from one to the other.) This sees their halt a few miles from James City.
1st Corps marches through Rixeyville and into Culpeper. (They have right of way over 2nd Corps.) They make it through the town but not quite to the crossroads where they will turn right (west).
This confirms the decision to have Longstreet retreat today - otherwise he would be attacked in Culpeper.
2nd Corps marches to Brandy Station and then to Culpeper, where they wait for 1st Corps to pass through first. (It could equally be argued that well timed marches would mean that 2nd could be through before 1st arrived, but I will assume maximum friction here.) This sees them march less than the full nine miles.
5th Corps marches two miles to Kelly's Ford, and then another seven miles to Stevensburg. The modern route takes a jack-knife detour and thus takes more than seven miles to get from Kelly's Ford to Stevensburg, but it appears that following the original route indicates that 5th Corps can camp on the outskirts of Stevensburg (even if not quite at the crossroads).
6th Corps moves to Bealton Station and marches via Rappahanock Station to Brandy Station. This is a journey of about nine miles (the exact distance depends where in the Bealton Station area 6th Corps bivouaced).
11th Corps marches for Kelly's Ford and bivouacs one mile from the ford itself, on the route 5th Corps was earlier in the day.
13th November:
Walker has to make a decision today about whether to resist 9th Corps - even if they didn't earlier, the US cavalry will be reaching Madison Court House today. My assumption is that he will march to Madison Mills instead of trying to resist an attack by a force more than four times his strength.
The shortest route is 11.1 miles, so Walker will get most of the way there on the 13th and cross the Rapidan on the 14th. (If he pushes he will cross the river on the 13th; either way, he has broken clean.)
Longstreet marches the rest of the way to Rapidan Station. He does not need to choose how to defend the line of the Rapidan just yet, but he will need to soon - i.e. during the 14th. I will examine the constraints on his defence on the 15th when we switch to the Orange County map.
9th Corps marches to the crossing of Robertson's River. They cross, but do not quite reach Madison Court House junction.
Sanity check: Waterloo to Madison via Amissville and Rixeyville is 36.2 miles to the junction.
1st Corps marches for Robertson's Ford, aiming for Madison Mills. Their total distance to the latter is 16.2 miles, so they will get there tomorrow afternoon (ahead of 9th Corps) and will thus cross first on the 15th.
2nd Corps marches for Mitchell's Station. They wait until 1st Corps has cleared the town before beginning their march and then take a parallel route along less major roads, and do not quite reach Mitchell's Station by the end of their march. (Their objective for the 14th is Rapidan, which they can make with another 6-7 mile march; thus they will reach it by the end of the 14th.)
5th Corps marches to Raccoon and Sommerville Fords, a distance of eight miles from Stevensburg. They could theoretically cross on the 14th, but will wait a day so the movement is coordinated (and so I can switch to the Orange County Map consistently...)
6th Corps marches from Brandy Station via Stevensburg towards Germanna Ford. They must interrupt or delay their march until 5th Corps has finished exiting Stevensburg, but the total distance from Brandy Station to Germanna Ford along the modern route is only 12.7 miles; even with how the roads have changed it cannot be more than 15 along the period routes. I will assume 6th passes through Stevensburg and halts six miles from Germanna.
11th Corps heads one mile to Kellysville and then turns for Germanna Ford. It's nine miles from Kelly's Ford to Germanna, so they stop one mile short of the Germanna crossing.
14th November:
Per the rules I previously established, this is when Jackson starts moving.
There are two possible routes that Jackson could take. One of them is to make essentially his historical movement.
Jackson's command HQ went:
21st: troops started leaving Winchester
22nd: Jackson and his HQ marched and went to Old Stone House
23rd: Mount Jackson
24th: Hawksbill
25th: through Fisher's Gap to Madison Court House
26th: having gotten ahead of the troops, near Madison Court House
27th: Gordonsville, redirected to Fredericksburg
28th: Orange Ct Hse
29th: Rode ahead of troops to Lee's HQ on the Mine Run Rd
30th: recce'd the area his divisions were assigned to
1st: Met the lead division at Massaponax Church
The important data point here is that on the sixth day of movement Jackson waited for his troops at Madison Court House; thus we can assume that Jackson's troops reached Madison Court House on the sixth march.
If Jackson took this movement with his first march on the 14th, his leading edge would reach Madison Court House on the 19th (presumably this would be DH Hill's troops, who started at Front Royal and had the least distance to march).
If on the other hand Jackson followed his previous instructions from Lee and marched via Swift Run Gap to Gordonsville, he would be delayed by several more days at least and arrive in the Gordonsville area.
Interestingly even if Jackson moved the moment that McClellan's main body began to march out of Warrenton (which is functionally impossible, he cannot get that information that quickly) and took the shorter route his troops would still not reach Madison Court House until the 15th; no matter how soon Jackson moves, he cannot arrive in time to help Longstreet hold the line of the Rapidan.
We can also assume that McClellan would have this estimate; in other words, McClellan would be able to tell that Jackson could not interfere with his operations in time.
Movements of the 14th:
9th Corps: marches to two miles short of Madison Mills.
1st Corps: marches to Madison Mills, and probably has time for a recce. (No marked road past Robertson's Ford on the detail map, but this seems to be because it's a map of the wrong county. The outline map and a map of Madison County both show it.)
2nd Corps: marches to Rapidan Station, and has time for a recce.
5th Corps: has time for a recce at Sommerville's Ford and Raccoon Ford.
6th Corps: marches to the Germanna Ford area, waits behind 11th Corps.
11th Corps: marches to Germanna Ford and has time for a recce.
We will now be ready to switch to the map of Orange County.
I will also provide a map of Orange County with the current positions of McClellan's corps "just off the map"; I invite people to suggest how Longstreet disposes his forces.
His total available strength is that his main body has 23,400 Effectives or 27,600 Present, Walker (retired from Madison Court House) has 4,200 Effectives or 4,900 Present, and as of the 10th half of Hood's division was at Gordonsville in smallpox quarantine (at 3,250 Effectives or 3,900 Present). This puts Longstreet as having 30,850 Effectives or 36,400 Present; I'm including both numbers because the ratio between these two is not the same as the Union ratio, and so we should consider both Effectives and Present for measuring to what extent Longstreet can fight.
As a reminder, each corps of Union troops is assumed to be standardized at 23,550 AP or 15,700 Effectives. This means Longstreet is best modelled as 50% to 80% stronger than one corps but weaker than two.
So: where does Longstreet place his troops? Any suggestions?
(If anyone thinks that Longstreet could oppose the corps movements I've outlined in this post, I'm also interested to hear it. The way I've had the Union corps moving is specifically intended to allow them to curl in behind any of Longstreet's possible defensive positions north of the Rapidan, but I may have missed something.)