The thing to remember, that I think alot of people forget is that the CSA was not unindustrialized at all, nor was it a poor backwards economy. To be sure the CSA was outmatched in every way but proportion of slaves to citizens by the north, but the state was still among the largest industrial economies in the world at the time. And with a surviving CSA likely seeking any edge they could I see them pursuing industrialization as much as possible. Probably as a means of countering the loss of revenue from selling Cotton to the British and north.I know Confederate States Navy battleships are popular in alt-history, but given the likely state of the CSA by the early 20th century (probably Southern Cone-tier for development/economy) I feel their navy would need to be looking smaller for effective defense against the US. My thought was they'd identify Tennessee as their key weak spot given proximity to the border and critical importance given the industry, agriculture, and transportation, and they'd thus develop plenty of river warfare vessels for fighting on the Cumberland, Tennessee, and Mississippi Rivers. What sort of craft might they develop?
Certainly they could probably make some fairly large river monitors as I believe as early as the 1930s, the Mississippi was navigable for craft up to 9 feet of draft as far inland as Minneapolis, replacing an earlier system of locks. I presume the USN might build river monitors of this size to counter anything the CSA throws at them by sea. My thought would be for the Mississippi, they'd develop ships that could do double-duty in both the river and the sea, with a fleet of torpedo boats and coastal destroyers that would have that 9 feet of draft. For a WWI destroyer, that would be about 500-1000 tons--would that be enough to act as both river monitor and destroyer from Cairo, IL to the Caribbean/Gulf of Mexico? Could you make it seaworthy enough to be a decent mini-commerce raider? I feel the CSN will be strapped for cash and need ships with a lot of potential roles, including the essential role of river defense.
The Tennessee and Cumberland could be integrated assuming the CSA builds the Tennessee-Tombigbee Waterway (expensive, but crucial to national defense). Early plans called for making a passage for ships up to 4 feet draft, but the modern waterway I believe has 9 feet. I'll assume the CSA is too poor for more than a 4 feet draft. I'd assume these would just be typical torpedo boats of the ra around 150-200 tons, but something the CSA could domestically build a sizable number of and use throughout their internal waterways and coastal areas.
Would this sort of Jeune Ecole doctrine work well enough for the CSA to beat hypothetical enemies like Spain while acting as deterrance for the US so they're far more careful with any potential blockade? Or anyone care to Springsharp or otherwise draw up decent designs?
What this means for their navy I cant say, but a surviving CSA would have the potential to be able to afford a not insignificant navy should they want to. Though they would be best to invest in a mostly coastal and riverine force, see stuff like the Austrian Danube river monitors. Though if they wanted they could also likely afford a few battleships as status symbols if they wanted.