This scenario assumes that General P.G.T. Beauregard, rather than being transferred west in early 1862 to take the post of second in command of the Army of Mississippi, is instead assigned to command of the Department of South Carolina, Georgia, and Florida, where he oversees the Confederate coastal defenses in that region (a task in which he excelled when assigned to it later in the war). Thus, he is not present at Shiloh in April 1862.
April 3, 1862--The Confederate Army of Mississippi leaves Corinth, Mississippi, at dawn, aiming to attack the Union army under Major General Ulysses S. Grant, which is encamped at Pittsburg Landing, Tennessee (in OTL, delays caused in part by actions of General P.G.T. Beauregard and his Adjutant, Colonel Jordan, delayed the advance from Corinth until April 4. Since Beauregard, in the ATL, is commanding in the Carolinas and Georgia, this does not occur). The Confederates arrive at their “jump off point” near Pittsburg Landing on the evening of April 3, and go into camp for the night.
April 4-5, 1862--The Battle of Shiloh. The Confederate Army of Mississippi launches an attack on the Union Army of the Tennessee, under Major General Ulysses S. Grant, at dawn of April 4, 1862. Confederate General Albert Sidney Johnston’s original plan is carried out (in OTL, it was changed by General Beauregard), and the Confederate Army of Mississippi attacks with Polk’s Corps on the left, Bragg’s Corps in the center, and Hardee’s Corps on the right, with Breckinridge’s Corps in reserve, the Confederate Corps moving up side by side in compact columns (instead of the formation ordered by Beauregard in OTL, where the Corps advanced in echelon). Johnston's plan emphasizes the attack on the Confederate right flank against Grant's left, aiming to capture Pittsburg Landing and separate the Union army from its gunboat support (and avenue of retreat) on the Tennessee River, driving it west into the swamps of Snake and Owl Creeks, where it can be destroyed. Johnston makes it known to his subordinates in no uncertain terms that the aim is Pittsburg Landing, and nothing must stop or delay the Confederate thrust toward that objective (in OTL, subordinate commanders were confused after receiving conflicting instructions from Johnston and Beauregard as to the objective…Johnston was saying Pittsburg Landing, but Beauregard envisioned an assault with the objective of driving the enemy into the Tennessee River…the opposite of what Johnston intended).
The attack is a complete surprise, and, despite their inexperience and disorganization caused by the heavily wooded terrain (much less than in OTL due to the attack formation ordered by Johnston, which allows the Corps Commanders to keep much tighter control of their inexperienced troops once the battle has started), the Confederate forces advance rapidly. Among the dead in the first hour of the attack is Union Major General William T. Sherman, who, having been roused from slumber by the first shots of the attack, is shot through the head while mounting his horse as he prepares to ride off and see what is happening. As in OTL, Union forces attempt to make a stand in the Sunken Road (the position which would, in OTL, become known as the Hornet’s Nest). But rather than allowing themselves to be delayed by Union troops holding out in this strong position, the Confederates instead cordon off and bypass the position (it is reduced by concentrated artillery the next day), and continue on toward their objective. Pittsburg Landing falls at 11:00 a.m., and General Grant is killed shortly afterward, as he tries to organize a defense of the Landing, when his party is surprised by fast-moving Confederate cavalry under Colonel Nathan Bedford Forrest. Grant‘s death means that Union command and control pretty much falls into chaos from this point on, and Grant’s Army finds itself effectively flanked and forced away from the Tennessee River into the swamps. The Confederates push them further into the swamps through the rest of the day, until, at about 4:00 p.m., a heavy, cold rain begins to fall, effectively ending that day‘s fighting. It rains all night, turning the fields and roads in the area into quagmires of mud. It also effectively dashes the efforts of the Union Army to construct defensive lines during the night.
The mud-soaked fields and roads caused by the previous night’s rains cause the Confederates to delay renewing their attack until 1:00 p.m. on April 5, 1862. General Johnston spends the intervening time reorganizing his troops and replenishing the ammunition of his men., and the Confederate attack, when it comes, is devastating. It is made all the more so by the fact that Breckinridge’s Reserve Corps, which was never committed to battle the previous day, is completely fresh and rested when it makes it’s assault on April 5. The Union Army of the Tennessee, pushed against the anvil of rain-swollen and impassable Owl and Snake Creeks, it’s morale destroyed by the defeats suffered the previous day and the death of it’s beloved commander, shatters under the Confederate hammer blows. Some individual division commanders (Lew Wallace is the most prominent of these) decide to go out in a blaze of glory, and fight until their positions are literally over-run, causing huge Confederate casualties. Most, however, seeing the impossibility of their position, simply surrender. A few units do manage to escape the trap, but, for the most part, the Army of the Tennessee ceases to exist by 6:00 p.m.
The Confederates have won a huge victory, but at a terrible cost…almost 13,000 Confederates are dead, wounded, or missing. The Union army has suffered far worse, however…over 15,000 dead or wounded, another 20,000 captured. Only 5,000 out of the original 40,000-strong Union army escapes to fight another day. It has been the bloodiest two-day period in American history up to that point.
April 6, 1862--Refugees from Grant’s Army of the Tennessee reach the headquarters of Major General Don Carlos Buell, who is, at the time leading his army to link up with Grant at Pittsburg Landing. Buell, hearing their reports that Grant is dead and Pittsburg Landing has fallen, decides to retreat back to Nashville rather than continuing on to Pittsburg Landing.
So what happens from here? Several questions come to mind...
--What would be Sidney Johnston's objectives in the aftermath of his victory? Johnston is shortly going to be reinforced by another 20,000 men (Van Dorn's Army of the West, ordered across the Mississippi from Arkansas). Does he try to reclaim Nashville and/or invade Kentucky? If Johnston later meets Don Carlos Buell in battle, who wins?
--What would be the possible international repercussions? Would such a decisive Union defeat and apparent end to the string of Union successes in the West be enough to bring in Britain and France on the side of the Confederacy?
--How would the Lincoln Administration react...would they take troops away from George McClellan and send them west to redeem the situation there, and if so, does that effectively scuttle the Peninsula Campaign?
Any other thoughts?