alternatehistory.com

2 May
Grant's forces attempt a breakout. The portion of the army for which small arms are unavailable is assigned to the artillery, serving as additional manpower, and this makes the guns much more mobile - letting them hit part of the Confederate lines with a high concentration of force, and break through to the north towards Goodlettsville.
A.S.Johnston reacts quickly, having the southernmost division of his army attack towards Nashville - which succeeds easily as most of the Union army has already left the city - and his men capture the bridge intact. Sending half his army this way, he has the remaining infantry concentrate to form two flanking columns and detaches his entire contingent of cavalry under Beauregard to head Grant off.

The running battle continues for several hours, with Confederate forces road-marching up behind the Union ones and the Confederate flanking columns interfering with any attempt by the Union to set up a blocking position. Beauregard and his cavalry are not able to make their way in front of Grant before Goodlettsville or to break into the column and scatter it, and Grant's vanguard set up at Goodlettsville as soon as they reach it - establishing a perimeter.
Johnston contemplates the situation, and decides to order a prompt attack - as little preparation time as feasible, so as to prevent Grant's men from fortifying their position or from retreating further north overnight. While driving them back to the mountains would be a significant achievement, he wants this army.
It takes until five in the afternoon for the Confederate artillery to be brought up, and - mindful of the time - Johnston has his men eat and recover their morale in the two hours of lull.
At ten past five, the Confederate guns open fire, bombarding a position on the crest of a shallow hill, and the infantry move in. Grant is trying to hold over five miles of front with 20,000 shooters, and has to keep some of them in reserve - so his line is thinner than he would like. (A two-deep firing line has two men per yard - he has enough for this, but it takes up well over half of his infantry.)


After the losses of the previous week, Grant has 35 smoothbore guns (mostly 6-lber) and 40 rifles, also mostly 6-lber. Those guns able to bear inflict many casualties on the Confederate attack, but the presence of the CS light guns being pushed forwards alongside their infantry (including many of the guns Grant's men had used last week) means that the Confederates keep coming longer than normal - they are heartened by their own artillery.

The first wave attack stops and ends up in a firefight at about 70 yards range, but the second wave twenty minutes later is Johnston's trick - it consists of the entirety of his cavalry, who charge home against a line already blasted by Confederate canister and all but unable to see them due to thick powder smoke. Several squadrons are nevertheless stopped by determined Union infantry, but the Third Division as a whole loses cohesion.

Grant's army is split in two by the collapse, and the main thing which will prevent a total surrender is the time. It takes long enough for Johnson to move in his own reserves to exploit the breach that evening is falling, and the Confederate general is denied his prize - two full divisions of Grant's army retreat on Springfield, with their Confederate opponents too disorganized to pursue, and fragments making up roughly one more division also filter out.
The impact on the Confederate army is considerable - their cavalry has been wrecked and will not be able to operate as a coherent arm for some time (the Confederate remount system is not able to supply remounts efficiently, consisting of the trooper providing his own horse) and the assault infantry have been badly chewed up, to the point that the total casualties exceed 4,000 killed and wounded.
The Union army, however, has been roughly halved in size. Grant now has 20,000 infantry left, around 9,000 of them without small arms, and the balance is mostly captured or wounded/killed. He has also lost most of his artillery.

Later historians will decide that both Grant and Johnston did not allow for their opponents making certain decisions, and that each missed opportunities. In particular, the Confederate cavalry should have been north of the river to begin with, while the Union would have been better served by setting up a narrower perimeter or perhaps, after all, arming some of their men with pikes to form anti-cavalry detachments.