Wolfshanze
CFC Historian
Technically, all ships obsolete... You can't really turn a Trireme into a Caravel or an Ironclad into a Pre-Dreadnought Battleship...Hey Wolfshanze, how come the Dreadnought doesn't obsolete? Shouldn't it go away whenever... what's it upgrade to, Battleships?... is available?
Wodan
However, I decided to do a little bit of a combo in my mod. I cut-slack to older ships (age of sail & ironclads), as they can upgrade to newer ships... while the big super-expensive ships of the modern age can't upgrade (Dreadnoughts and Battleships are both dead-end units, as neither can be upgraded to, or upgraded from). It's a little something in the mod to represent the enormous cost these ships required from nations... it was also quite intentional to show that even "out of date" ships had use... as many WWI dreadnoughts saw service in WWII alongside more modern battleships.
Essentially I didn't want to stifle ship building from the early ages, as economies are usually in flux and it's hard enough to build a fleet, so I allowed upgrades as per the normal civ... but in late-game (when you should have a strong economy), I decided to tighten the screws a bit, and force a little more realism (like using older ships in current wars... dreadnoughts in WWII, etc).
It's all intentional... everything has a purpose... there is a method to my madness.