"...the Army Staff Office prided itself on its planning and the first wargames were carried out in the spring of 1905 modelling "HHH," with few if anyone imagining even at that time of grudges over Yankee battleships and the contest for the Caribbean fruit and sugar markets that in eight and a half years the Confederacy's carefully devised strategic war plan would be executed to the letter.
HHH's assumptions were built on a series of Confederate strategic assumptions, some correct and some horribly wrong. In its original incarnation, the Army Staff Office presumed that they would fight the Union alone or, at best, with overt Chilean support at sea; explicit alliance from any other powers besides the Chileans was not considered and it had no political gamesmanship, instead existing solely as a wargaming exercise. In other words, if France or, in a less likely case, Britain were to assist the Confederacy, it would be quietly, as they had done in the initial eighteen months of the War of Secession. Spain's recent defenstration by Japan also eliminated them as a potential ally to the Union and thus it was seen as a likely fight between "brothers." The benefit of this presumption was that it made ASO use more conservative estimates of manpower, mobilization, and logistics; the downside was that ASO still presumed that HHH could produce a head-to-head victory.
This assumption was built on a cracked foundation of flawed data and extreme prejudice. It was no secret that the Union had elected to develop itself as a naval power after Havana (whose expiry in 1913 Confederate politicians had started discussing well in advance, already leery of the inevitable negotiations to come) had rendered the Monroe Doctrine a dead letter which they were reliant upon other Great Powers to enforce, and had thus neglected its Army for a variety of reasons. These reasons included a fear of standing armies leading to autocracy, politicians in coastal states enamored with feeding their campaign donors juicy naval contracts, rapprochement with the Confederacy in the 1880s creating a sense that a land war in North America was unlikely and, perhaps most importantly, a political class reluctant to reward an Army establishment that had proven in the War of Secession and in the Indian Wars, Utah Uprising and Boxer Intervention to be comically corrupt, incompetent and craven. A handful of staff level reforms had been successfully pushed by the late President Custer and some administrative changes had been implemented in the brief tenure of War Secretary Elihu Root but the US Army of 1905 was still the infighting, poorly-equipped Indian constabulary that had had to be bailed out by the Japanese at Tangshan when fighting off Chinese civilians with pitchforks and spears. The only positive that had come out of the Boxer War for the United States was that its forces had not been drawn down; it retained its postwar strength of 76,000 men [1], primarily in its six cavalry regiments of about a thousand men (including officers) apiece in the territories or harbor garrisons. This was partly as a sop by the US Congress to insistence by the Army that having an army smaller than that of Norway was a disgrace. Still, it was the Navy that was lavished and US war planners had made it all but public that they presumed that in the event of a conflict in the Americas - either with the Confederacy or Chile again, potentially both - their plan was to rely on the Navy to secure all major ports and then choke off all commerce from there, and dare the Royal Navy or Marine Imperiale to stop them.
ASO had considerable doubts that the "damned Yankees" could or would actually do this and though they could not dismiss the Union naval building plan as bluster (nor the very competent US Marines), they were confident that the British or French could successfully stare down a Union blockade if it came to it, and thus the war would really be won on land, hence HHH - Hit, Hold, Harass. [2] Between Kentucky and Virginia alone, the state militias of those critical border states could mobilize close to 40,000 men within days of a conflict breaking out; North Carolina's additional 17,500 strong state militia could be transported by rail to northern Virginia days later, and a force nearly as strong as the entire US Army would ten days in be ready to cross the Potomac at several key points, in particular Harpers' Ferry, to perform the Hit - an offensive incursion into Maryland to threaten Washington DC from west, north and south. Confederate spies in Baltimore were well aware that Maryland, despite being a border state, was one of the most tax-averse and conservative in the Union and thus had one of the smallest and most poorly trained and equipped state militias in the Union; before the US Army could properly mobilize its small professional force, Maryland would be mostly overrun.
In Kentucky, the key was to perform the Hold - preventing crossings of the Ohio, primarily at Covington and Paducah, while bringing up the rest of the 100,000-strong Midlands state militias to bear and repelling the Union on the advantageous defensive. As veteran and green volunteers alike poured in - not to mention that ASO estimated as many as 100,000 reservists and militiamen from the southeastern coastal states and also members of the professional core of the 25,000-strong "direct" CS Army based at its various forts that [3] would be ready to fight - their most conservative estimate suggested that between the eastern and central theaters of war, the early weeks of a campaign would have close to a quarter million men ready to do battle, and tens of thousands more conscripted or volunteering to fight who would be ready within months.
The last part relied on the militias of the Transmississippi warding off land attacks into Arkansas, Texas and Arizona (where much of the professional CS Army's elite cavalry was stationed) across vast, difficult terrain by the Union Army in what was anticipated to be a distant theater of the conflict, where they would be drawn to the end of their logistics and attacked aggressively in a hybrid conventional-guerilla campaign that would bleed them of resources and morale before being surrounded and destroyed at a time of a commanding officer's choosing. This was the last "H" - Harass. The three-pronged plan was innovative in its considerations of a multi-theater war, utilizing the state militias as the mobilization tree of the Army as a whole after the forces were federalized in the immediate hours after a declaration of war, and using train timetables and careful studies of geography to assume how far their armies would advance on what days. ASO was particularly confident that, by gaming out a variety of contingencies in their campaigns and designing defensive and offensive logistical lines in advance, in addition to the overhauls of doctrine at the military academy in Montgomery, a poorly-planned debacle such as the intervention in Cuba would not repeat itself. The CS Army was a very different beast than the ragged expeditionary force of thirty years prior and was continuously improving by the year.
Of course, even terrific war plans collapse under white hot heat of actual battle, and HHH for all its modern innovations that were being repeated in Europe by German, French and Austrian military planners was nowhere close to terrific. Its data correctly assessed the numbers of the professional US Army and the Yankee state militias but as those charged to execute it eight years later discovered it grossly underestimated how rapidly American volunteers could be gathered, taught to shoot a rifle and then sent off to kill Dixiemen, and its attention to logistics was based more around the length of supply lines (it never envisioned a Confederate advance beyond central Maryland, for instance, at least in its initial versions, because it correctly deduced that much further would be difficult to sustain and wrongly presumed that the Union would sue for piece the moment "God Save the South" could be heard in Washington) than around the armaments production capabilities. And this was part and parcel of its most fatal flaw - ideology. Industrial production, logistics, training, all these things were not considered outside of the initial ninety-day campaign ASO envisioned because they could not fathom that the feckless, urbane and incompetent Yankees would not simply collapse under the fire of the chivalrous and martial Confederates marching on their soil and fight on any longer against such a plainly superior - militarily and indeed morally - foe..." [4]
- Bound for Bloodshed: The Road to the Great American War
[1] If you can believe it, the OTL US Army that included the Southern states was about half this size pre-WW1
[2] Consider this the initial development of the Deep-Friend Schlieffen Plan, built just as much on optimistic assumptions and navel-gazing as the real item. Can also call it "Dumb Schlieffen"
[3] Recall that the Confederacy has robust and strong state militias that serve as the backbone of their army in a way the underfunded, labor union-shooting state militias of the Union do not, but there is still a professional core (primarily cavalry), and there are strong societal expectations to serve in the militia either actively or as a reservist to be a "real man" etc
[4] This is your brain on a combination of navel-gazing victory disease built on the same insufferable Lost Cause tropes from OTL only worse, since here they won