I doubt any of the countries listed would move to heavier guns than they did, because none of them have a need to drop a heavy shell right on top of a bunker at a range surpassing lighter-caliber artillery, which was the reason the Mark 71 was developed to begin with. The only place they'd run into that sort of defensive setup would be an amphibious landing on USSR soil directly, and for various reasons none of those countries would ever do that.What happens worldwide if the US starts shipping 8 inch guns? The RN started using the Mk8 4.5" gun from 1973 and eliminated it in 1980 with the Type 22s. Would they instead maybe revamp say the 6" gun used in the Lion, Tiger and Blake and fit it to the Type 22? Would the French go for something much bigger than their 100mm? The Russians and Italians had very powerful 130mm/5" guns, but would these be seen as enough when the US had 8"?
Modern unit would be a modern 5" or the OPs 8" firing smarter than me ammo and then something like a multiple Brimstone/Sea Spear or similar in a VL launcher or a modern HellfireL like missile that retained a 'human in the loop' (that's how we fights the wars today) target allocation - ideal for both deliberate targeting and defence against littoral Swarm attacks and control and the ability to operate multiple UAVs for detection and targeting.
If its performing NGS then it is operating in a littoral environment and therefore needs to be able to defend itself verses a swarm - note 'defend itself' not seek out and wipe out the local sea borne militia.I'd skip trying to add the Boghammer role for the Carronade update. It'll add expense and time. The goal is preferably a cheap, small crew requirement, semi disposable craft, that's capable of dealing out a fuckton of rockets against enemy shore defenses. Perhaps go say half the size or 75 percent the size of the Carronade and go with say 4 double eight inch rocket launchers. Pretty much anything that's going to be going close in to shore to bombard any sort of even mildly defended beach is going to be a death zone for said craft.
For the "Boghammer Killer" go with something like an enlarged Cyclone equivalent equipped with a large auto cannon (maybe that combination 25mm Chain gun and 40mm grenade launcher some of the Cyclones have), some mounts for machine guns, a number of stingers, and mountings for say 15-30 missiles around the size of a ATGM (Sort of like the Javelins and Griffins they're armed with now). Their supposed to operate under the extended air coverage of aircraft and Aegis ships equipped with long range SAMs. Their goal is to clear the road and blow Boghammers and other smallish armed speed boats to ship.
Probably cheaper to build two seperate relatively small batch (especially since one is essentially just a modified cheap landing craft and the other is an enlarged version of a gunboat/patrol boat the US already built a dozen of.) then trying to build another general "one size fits all" ship. That's what got us the LCS class.
If its performing NGS then it is operating in a littoral environment and therefore needs to be able to defend itself verses a swarm - note 'defend itself' not seek out and wipe out the local sea borne militia.
Modern operations are not going to allow unguided rockets (I am not familiar with 8" rockets? is this a current weapon system?) - any such attack is going to require 'human in the loop' targeting because otherwise things are more likely to look bad on the evening news.
If its bunkers you are destroying then the Tomahawk would be the creature of choice and probably not fired by this platformI mean most MLRS systems still use unguided rockets. Some obviously use more advanced targeting systems and even "unguided" rockets are more likely to be more accurate just because everything else is and the one calling in fire support can provide say GPS coordinates. Similarly even for unguided NGS from say a Arleigh Burke the 127mm Shells they're firing are still mostly "Dumb"rounds. Same with regular land tube artillery. Yeah their are some guided rounds but for the most part any shells fired are still going to be "dumb".
To my knowledge no eight inch rockets aren't current in use. I just used them as an example since the original USS Carronade used 5 inch rockets (I'm not sure if they were the same rockets used by the old Landing Craft Rocket used during WW2 or were a new design). But I figured a originally "dumb" eight inch unguided rocket isn't going to be terribly expensive to develop or produce.
In regards to the "evening news" the entire role of a modernized Carronade wouldn't be to say provide pin point fire support to fighting in say a civilian urban enviroment. It'd be to go in close to a contested beach head and absolutely swamp the area in unguided rockets (mostly HE, FAE, or potentially cluster bombs) before the troops hit the beaches. The pinpoint fire support is provided by either aircraft, drones, cruise missiles,or less likely actual naval guns. The Carronades job is much like the original Carronade guns. Be cheap as shit then get in close to the enemy and absolutely blow the shit out of them to help suppress the defenses and then let the more expensive and precise systems deal with what's left. The crew complement should be as small as possible (really ideally it should be a drone ship) since pretty much anything going that close in in a modern contested amphibious assault is going to get slaughtered by a combination of the defenders tube artillery, ATGMs, ASMs, MLRS systems, sea mines, boghammers, and everything else that can be thrown at them.
If you do want longer range then you could go for a larger initially unguided rocket (Say instead of the original 5 inch designs for for something like 8inch-11 inch rocket) develop laser guided packages for them later. If you're feeling adventurous maybe even develop something like a laser guided rocket assisted depleted uranium sabot round to tear into bunkers.