I really like this idea. Gives a reason to not simply spam the entire ship full with cannons. Though maybe 3x3x3 might be a bit to restrictive? Then again, it would require to get real creative with some designs.

1x1x1 would be better, just make the base surrounding the Connector port a set of module ports. Also an upgrade for anything in a game should never be "quite weak", it should be something that ENCOURAGES the player to use it rather than merely existing as an afterthought.

Definitely an interesting idea. Although I'll have to talk with Mexpex about it, he still maintains the art side of the mod himself. I do have some experience with it, but he holds the original art assets.

Potential for this could include: Turret health (lets say polarized armor?), turret rotation speed, reload speed, rate of fire, and less plausibly AI tracking range

@Whaddageek
By "quite weak" I was talking about the durability of the module. If it is able to sustain a lot of damage, players could just put it on the outside of the hull. My intent was to ADD an engineering challenge, for players to make room for vital modules.
Think I should make it clear that I dont think turrets should be very useful without upgrade modules. Their baseline stats (RoF, Rotation, etc) should be like 1-10% of their current levels. This addition would be a downgrade to the turrets as it, but one that I think would improve the overall feel and engineering challenge.
Going of of that, doing a 1x1x1 would not be quite enough to create that challenge, as it would simply replace the armor block that would be placed below the turret base. A 3x3x3 creates a real challenge, and makes the weapons a much larger part of the vessel.
IRL when designing warships (I have no professional knowledge of this, but it is a topic that I have spend a lot of time on), the entire vessel is designed around its main weapon systems (and deploying those weapons).
Currently, turrets are just slapped on, with little to no though of what is below it besides the relative small logistic system.

@PhoenixTheSage
Glad you like the idear. I really hope that you will be able to take a stab at it, and I would love to be included if you get that far.
For possible modifiers, I think that health would be a bit non-SE like, as that is always based on componets of the piece taking damage. I can appriciate the "polarized" being used as a tech-splanation for it, but then why would that tech not be used for other systems on the vessel?
I agree with Rotation, RoF and Reload. Perhaps even maximum rotation angle.
A quick splattering of idears for possible bases (with the "Full Base" being the only one I really would like to see, and the others being a nice addition).
= Assault Base =
3x3x2
Rotation Angle 90 degree; Rotation Speed 125%; RoF 100%; Reload 100%

= Limited Base =
3x3x2
Rotation Angle 270 degree; Rotation Speed 100%; RoF 100%; Reload 100%

= Compact Base =
3x3x2
Rotation Angle 360 degree; Rotation Speed 75%; RoF 75%; Reload 75%

= Full Base =
3x3x3
Rotation Angle 360; Rotation Speed 100%; RoF 100%; Reload 100%

= Interdiction Base =
3x3x4
As "Full Base", but Rotation Speed at 125%

= Bombard Base =
3x3x4
As "Full Base", but Reload Speed at 125%

= Dampner Base =
3x3x4
As "Full Base", but RoF at 125%

Just a asci mock-up of design of the 3x3x3

top
XXX
XCX
XXX

center
XCX
EEE
XCX

bottom
XXX
XCX
XXX

X=Solid "block" with no special function
C=Connector and modul attachment
E=Empty, as in internal corridor

Oh god no, the worst thing you can do is cripple something's baseline's levels just to add an upgrade system that's even MORE expensive to make it 'better'. It should be something to IMPROVE baseline specs, not brutally nerf the whole thing into being worthless.

@Whaddageek Fair enough you disagree.

Okay, let me put it another way;

Why would you bother with something expensive that does barely as much damage as a Missile Turret (if THAT), nevermind firing far slower, AND have to add modules on top of that just to get a single cannon anywhere approaching decent on top of that, when you could just build far more Missile Turrets on the cheap? It is not a good investment in resources.

@Whaddageek
As I see it, thats an entire different acpect. Balancing the weapons is ofcource important, and I trust the developer to keep the weapon balanced. However, my suggestion was based on the need for turrets to take up more space In THE FIRST PLACE, as I feel that there is no challenge in fitting large weapons to ships, and it feels "unrealistic" when compared to how real-world turrets take up a lot of space below deck.
If the base stats of turrets are not changed (if modules are added), players are not forced to find the additional space.
Ofcource this could be done by just changing the size of the turret itself, but then you would have one large system with the durability to resist many hits - by doing modules, players must find a way to protect the system.

You still need to strike a balance between what's realistic and what is actually FUN for players in both use and their own ship designs.

The internal components of a battleship cannon all revolve around pumping ammo into the thing, and that's what conveyors do anyway. You're just unnecessarily cargo-culting several decks of ammo-handling space because 'that's how real battleships used to do it', when the actual working mechanisms of the cannon are what you already have: the topside cannon mount.

Here's a better way to do it;

Start with the Mk.3 as it is now, go with, let's say, all 24 spaces beneath it used for upgrade slots. Make the upgrade blocks 2-sided. Now you've got a reason to build down into the ship, because your base cannon's pretty decent, but you can make it EVEN BETTER by tacking mod blocks in.

It's okay to have something become better/super-powered because you crammed 5x5 stacks of damage+ blocks in, because that's how you chose to build it and are rewarded by your own design efforts. The onus is on anyone encountering it come up with a defence, because that's an ENGINEERING challenge. they have seen this guy with his overpowered cannon, and now the question is one of how to build something even better themselves to kill it.

@Whaddageek
I do see the value of that approach - somewhat like From the Depth. However, I still feel that for S.E. and MY PERSONAL taste on how it would improve my experience, a single large module would be better.
Ultimatly its nothing more than suggestion to the modders. If they choose to invest time and energy towards something like your or my idear I would be very greatful.
I am happy to hear of any additions or modifications to both idears, however I dont see it being benifitial that we keep crusading for our own approach.
@PhoenixTheSage
To the modders I would just like to say that I would be thrilled to be involved in any way if you do go ahead with this. Im totally fine if Whaddageeks approach is more to your liking.
I am currently doing an escort vessel, where I will simulate the modules using light armor blocks and conveyors, though adding blocks with no "real" function feels a bit wonky.

Fair enough. Off-topic, but if you want to get an accurate simulation of battleship cannon internal workings, why not just add a Large Cargo Container beneath the cannon to hold its ammo? Have a Sorter leading in from the rest of the ship to force ammo into its magazine, a second leading into the cannon to auto-feed it from the container.

I have though of that, but I would love to have the "module" touching the turret base directly - and that creates a problem with airthing seals using a large cargo container, and doing 9 small ones seems silly. Perhaps I will try to but is just below deck, simulating a 3x3x4. Still working on the hull and access paths, so I dont have to deside right away.