Yeah...At the time of typing i was horizontal and half a asleep. Keep the ship of the line and add an armoured frigate or boost its strength when a tech is researched?
I'd prefer to ditch the SotL. I just don't see what it offers over a Frigate. If there's a need to show that Military Science won naval battles, I'd rather just give an attack bonus to the Frigate at that tech.
So, with the addition of a Cruiser unit, the naval upgrade paths would look like this:
Galley -->
Galleon+ 4

, 3

-->
Transport 16

, 5
Trireme -->
Caravel 3

, 3

-->
Frigate++ 8

, 3

-->
Armored Frigate+ 12

, 3

-->
Cruiser 16

, 6

-->
Missile Cruiser 24

, 7
Cruisers and Missile Cruisers gain access to Interception promotions.
Missile Cruisers have a 30% base interception chance.
Cruisers gain +50% to attack and defense vs. all surface ships.
Cruisers and Missile Cruisers gain the Sentry promotion for free.
Destroyer 20

, 5

-->
Stealth Destroyer 24

, 5
Destroyer units are immune to First Strikes.
Destroyer units gain +100% to attack vs. Submarine units.
Dreadnought 20

, 4

-->
Battleship 40

, 5
These units inflict Collateral damage, and have a base 50% withdrawal chance.
Submarine 24

, 4
Attack Submarine 30

, 5
Both submarine units gain some First Strikes, and have access to the Drill promotions.
Carrier 16

, 5
+ gains a +1 speed bonus at Steam Power.
+ gains a +50% bonus when attacking at Military Science.
- - -
Differences from previous:
- Roles defined for Battleship, Cruiser, and Destroyer.
- Battleship is anti-ship and anti-stack.
- Cruiser is scout, air defense, anti-ship (mop-up).
- Destroyer is anti-sub (and perhaps mop-up).
- Carrier is air attack.
- Subs are anti-ship, with Drill they will tend to avoid collateral if in a stack.
- No more torpedo boat: that role goes to the Cruiser, which is a better upgrade unit anyway.
Design Goals:
- Now that everything upgrades to a Cruiser, there's an opportunity for anti-Cruiser units to shine (Subs, Fighters, and Battleships).
- Privateer also upgrades to Cruiser (via Armored Frigate). This means there's no more point in stock-piling Privateers just for the free promotion, which was icky metagame thinking.
- Role matters: what proportion of your ship production goes to Dreadnoughts rather than Frigates?
Thoughts?