Thanks again. I just wondered if a decently organised and officered army would have shortened the ACW and lessened the carnage( I am NOT impugning the intelligence or bravery of those who did just their experience). Obviously it would have done but conditions were not conducive to it with the USA set up as it was at that time, and to change that requires revisions of the constitution and governance back in the 1780s and 90s, not for what I was looking.
Actually I think it is not all that much needed to significantly improve the availability of trained manpower. The Regular army was really tiny and even a modest increase in absolute numbers could have multiplied the number of available officers and NCOs. For an increase in the reserves it is even easier. You have to see it fundamentally on the level of individual states. Iotl few states had reason to keep an organised militia, much less a system of organised reserves and the volunteers were formed on a local ad hoc basis. Your example of increased tensions with Britain imo is a decent pod for a short TL. As it is entirely improvised it would need a serious review and fleshing out before I would call it well founded, but it can illustrate the idea:
Some minor problem of the Oregon dispute is not solved and crisis reappears in 1854. Tempers run high enough that Britain reinforces Canada. The governor of Connecticut gets concerned that the British march again on Washington and the time for forming and training volunteers may be too short. To be better prepared the legislature decides to permanently keep an infantry regiment active. Enlisted men volunteer for a two year term, thus each year one batallion will be trained and one be active. Reserve officers have to serve twice the time. Core officers and NCOs are career soldiers. Command is given to the former Brunswick officer Adolph von Steinwehr who establishes a strict training plan following the priniciples of his old army.
Tensions continue into 1855 and British warships are rumoured to cruise in front of New York. Franz Sigel raises a volunteer force of German immigrants as quick reaction force in case of an invasion. The legislature legitimises it and offers pay under the condition to open it for non-Germans. Sigel is confirmed as commander of the new infantry regiment. Later that year an artillery battery under the former artillery lieutenant Frederick Salomon is added on Sigels initiative. A similiar rotation and training concept to Conneticut is established
Within the next few month´ other states follow the example of those two. Training standards, strength and equipment greatly vary. On one end is the New Orleans City Militia of Brigade strength with a 6 month service term for everybody (formed due to a hugely popular remembrance of the 1812 battle), on the other the Rhode Island Guard battalion with a 3 years term of service for enlisted.
Over the course of the year the tension with the British Empire are solved. But most of the formations are not dissolved, be it through inertia, economic reasons or a genuine acceptance of their role.
In 1857 several Southern formations agree to use the VMI standards for their officers. The next year the New England states, distrustful of Southern intentions, agree on common standards for officers as well.
At the outbreak of the civil war, almost the same time as otl, the reserves are the first to be activated. The Union that way gains 14 well trained regiments, named as distinction to untrained volunteers "volunteer guards". The rest of the trained reservists are used as cadre for volunteer regiments. The confederacy integrates their 16 trained reserve regiments directly into the regular army, but otherwise uses them the same way.