alternatehistory.com

29 June

McClellan recieves the messages from Porter informing the general of his change in plans. McClellan is initially angry, but after checking the map concurs that Porter had to shut off the possibility of Confederate troops taking Mechanicsburg and cutting off his army. However, this makes it all the more important to leave a rearguard - his men will desperately need time to entrench at Chambersburg.

As McClellan activates the orders for McDowell's corps to fall back, Lee's artillery fires off a sudden sharp cannonade on the western flank (which is Keyes' command). This is not followed up with a full assault, but causes disruption as men man the embrasures to defend against a potential Confederate attack - something made worse by the probing rifle fire of Cleburne's skirmishers.

Lee hears about the withdrawal of McDowell's corps, and has the relevent Confederate commanders prepare for an attack. He also orders troops readied to advance along the rest of the line, in sequence. This preparation takes an hour or two, and by the time it is ready to execute Keyes is also vacating his position.

For most of the afternoon of the 29th, Lee's echelon attack takes place. The assault is very similar in some ways to those that took place fifty years ago in Europe, with Cleburne's skirmishers taking the part of the voltigeurs in clearing the way and the Confederate assault rolling forwards behind the covering rifle fire. (One of the key differences is that Lee's men do not use the column - instead they advance in line, a probable miscalcuation but one which does not have any real effect on the outcome of the battle.)

Sumner's II Corps are hard pressed to hold their positions, and McClellan detaches some of III Corps (Heintzelman) to reinforce this rearguard - it will mean the extra division of troops is lost, but the rearguard collapsing early would probably lead to the loss of his whole command.
He also leaves all of III Corps' artillery for Sumner to use, as Heintzelman's men will need to move fastest and the extra artillery will hopefully make all the difference.


In the end, by the time the Confederate assault peters out, Lee has been frustrated. Pickett's men on the far eastern flank have managed to work around and cut the road north - behind III Corps - but Sumner is still holding out, having drawn back his men into a 'hedgehog' astride the main road and covered by liberal use of artillery.

Unable to pursue McClellan closely, Lee intends to crush Sumner as quickly as possible and then follow up to Chambersburg.






30 June


At Mechanicsburg, Porter wins the race to the town. His men are tired, having route marched about fifty miles since Chambersburg, but take interim positions and begin fortifying them - relying heavily on choke points through the hilly terrain to the south of the town itself, and also on the labour of much of the nearby population (who are quite panicked by the thought of Confederate cavalry arriving.)
Fortunately for Porter, the Confederate cavalry who indeed arrive a few hours later are also tired - they have cut a wide swath, but many of their horses are in desperate need of rest and the men themselves are sometimes close to falling asleep in the saddle. As such, Stuart does not launch an attack today, wanting his men to be in good shape.

An unexpected bonus arrives for Porter in the middle of the afternoon - several trains of infantry, coming from all over the country. These are about three thousand taken from the east coast (small numbers from each garrison, in general) and another few thousand from the men defending the southern shore of Lake Erie. While small, this nearly doubles Porter's front line strength - and the new troops are fresh.

Further south and west, McClellan has sent I Corps north to Mechanicsburg to shore up the line there. The rest of his men are resting after their march north, and some fortification of Chambersburg is taking place, but McClellan worries about their morale - being so outmanoeuvred by Lee has done a lot of damage to his hard-won esprit d' corps, and not only is rescuing Sumner's men unlikely in the extreme but defending Chambersburg against Lee's army seems a dicey prospect.
And there is that Confederate division well out on his western flank, as well.

At noon, McClellan makes his decision - fall back up the valley. This leads to a loud argument with Heintzelman and Keyes, in which McClellan makes the point that he would rather sacrifice a few hundred square miles than have his army ripped to shreds by Lee. In particular, he asks the two corps commanders which of them plans on leading the next rearguard.
After hours of debate, a compromise is reached - the defensive positions outside Chambersburg are set up, in case it is possible to hold, but they are also made as hard to pass as possible and food is withdrawn to Shippensburg. The intent here is that a Confederate attack on Chambersburg would be fought, but if it began to look like it would succeed then the Union would withdraw (and leave nothing that would make the Confederate pursuit easier).


Sumner's pocket contracts hourly as Confederate sharpshooter fire and artillery picks away at his strength. The general himself is wounded early in the process, but stays active - having his broken arm splinted against the pain.
Lee offers terms near sundown, and Sumner refuses - he will delay as long as possible.



(This turned out huge, so I'm going to do another one for the naval side of things.)