I'm currently testing the following and will post an update to the units/text files when I think it's working as intended (I would still need artwork as I'm just using destroyer and battleship art).
1) Adding a Modern Frigate at Nuclear Fission (same as Missile Destroyer. Might move the ModDD up one to radar as it replaces ironclads now),
75,
8, extra sight, ASW bonus, melee class upgrades from DD. (Notes: I left a sight bonus on both destroyers, missile capacity on Mis.DD, and any ASW bonuses, for now).
2) Adding a Dreadnought at Dynamite (same as Artillery, I may move this back a line),
38,
50,
4, capital class upgrades from SoL (requires coal). I also reduced the iron requirement on SoL to 1. I'm not sure it's necessary to trade that off as you can still use land units with iron usefully for a while (until rifling) when they appear and they're not extra ranged like later capital ships to where frigates (and galleons) aren't also a viable option.
3) Moved Ironclad to a ranged resourceless from capital class with a slight reduction in strength values. Moved DD to melee
c5strength: 60, moves 8).
4) Moved submarines to ranged. No upgrade path. Increased in cost from GEM, left the defence/attack promotions, removed sight penalty, adjusted strength/ranged to compensate for free promos (raised melee value, lowered ranged. May just remove the promos, and adjust strength to compensate for ranged defence modifier on most ships).
5) Slight adjustments in combat values.
a) Rounding for simplicity
b) slight adjustments downward in melee ships
. (17, 30, 40, 60, 75, down from 19, 35, 44, 60+, 91+). Combination of move after attack, siege/anti-ship promotions, and higher speed should be enough with moderate increases in strength rather than significant increases. This can be rebalanced as needed. Thal also has a change where they are cheaper to maintain, and where ranged ships have a ranged defence modifier, making melee naval units more powerful still.
c) -1
adjustments downward for vanguard units and a slight reduction to the camaraderie promotion, but that's another thread.
I will also probably add an intercept chance/AA bonus to carriers (and check to be sure subs can't attack cities directly).