A 'carronade' is a term from the age of sail. Due to a variety of factors warships were generally standardised on the concept of 8, 16, 24 and 32 pounder gun batteries. Frigates were the lightest of these ships, small, agile and generally equipped with a single deck of guns no heavier than 16 pounds. If they had another deck, it was probably 8 pounders.
This made these frigates fast ships and excellent for scouting, but not really suited to a battle line.
Ships of the line however carried batteries of big guns, often on 3 decks that were loaded from top to bottom with 16, 24 and 32 pounder guns. This made them very powerful in naval artillery, but slow and lumbering at best.
So what happens when you take a ship of the line and tear off the top gun deck?
Well, you get a heavy, slower frigate than normal that's absurdly overgunned for its size with its batteries of 24 and 32 pounders, but with crap for range. These ships were called carronade frigates.
And that's kind of the role the Plasma Carronade has in game; a big weapon system that's rather close in and horrifyingly good at breaking other ships.
Ummmm based on my recollection from playing Wooden Ships & Iron Men oh so many years ago (and reading Horatio Hornblower) I think this explanation is a little bit off. It looks good right up until "These ships were called carronade frigates" part at the very end.
The short version: What you've described is a "razee frigate". Carronade is a niche type of gun, distinct from a "long gun", which has a shorter barrel and is of heavier caliber for the same weight.
The long version:
My recollection (and here are a couple of links to back it up
https://en.wikipedia.org/wiki/Carronade https://www.eurobricks.com/forum/index.php?/forums/topic/6025-cannons-vs-carronades/ http://artillerymanmagazine.com/Archives/2004/carronades_sp04.html) was that carronades were much shorter guns that could fire much heavier shot for the same weight of barrel and hence were more inaccurate, i.e. like designing a sawed-off shotgun in a larger caliber to take advantage of the weight savings.
The 3rd link (to artillerymanmagazine) above was the most interesting (in the "I learned something" sense) to me - it's got a good discussion of how the accuracy issue is more nuanced than simply "short barrel = greater angular dispersion".
So Carronades are actually a different type of gun than "long guns". BTW, cutting off the top deck of a ship was called "razeeing" (
https://en.wikipedia.org/wiki/Razee) - I think you may have been thinking of "Razee Frigates" (as opposed to "carronade frigates) in your description.
John