Well I do have this idea for a very heavy siege gun (300mm+) that was stabilised with 6 hydraulic legs and could fire in any direction without needing to be moved that could function as a railway gun, coastal battery, heavy fortification weapon, naval artillery or added onto the deck of a carrier without needing a gun mount on the ship itself. The legs could allow it to fire at odd angles or on uneven terrain and not require specially developed tracks or anything else in order to fire. Not sure how feasible it would be (beyond providing a cruiser grade gun) but how feasible is a rolling deathball?
For some reason, probably the legs comment, I am picturing a Metal Gear. Still, having something as versatile as you are listing is far likelier to be complex, maybe twice over, and require a large amount of resources. May want to stick with something simple in coastal artillery we could mount to our ships.
Maybe this:
https://en.wikipedia.org/wiki/40.6_cm_SK_C/34_gunMay want to wait a bit further into the future for that, though. Get through the plan of Torpedo, RADAR, Destroyer, Carrier first.
Yeah that is battleship sized isn't it... Maybe 255mm then. But either way having something much bigger than them (in terms of artillery) is a good thing. That said battleship grade coastal batteries would deter naval invasion right?
Cannala's largest artillery is (I think) a 6" (150mm) piece called the Nightstorm Howitzer. This is larger than ours, which is only 100mm. Certainly, developing a truly large gun would be advantageous... but if we aim more for a carrier doctrine, we may not actually need the big guns? I mean, if we can make it mobile on land like you describe, that would be useful, but may prove impractical. I dunno.
Can we see the Cannalan design list somewhere, or is that considered spying before the game starts since we've got a free design?
If it is there old game's final listings, I don't think it would be considered spying since they have ours they can look at as well and several on both sides have likely already seen those lists, and there would be people just wanting to read the game. It isn't the list they are using, but we can guess based on it. Just don't go past the final turn just in case they discussed anything in that thread.