Well... first off, the question to ask is if you want an all big gun (for the flash effect and the fun of rolling massive numbers of dice) verse a missile arrangement. I only ask this because designing these ships is a bit of a math monster due to lack of an easy program to work them up... nothing insurmountable, just wanting to know what is desired before hammering away at the rules and still making mistakes, as earlier examples are prone to displaying. They are still kinda nebulous on how much of what should be carried to keep one serviceable (as everyone's knowledge is not equal nor information to fill in the gaps readily or easily available).
Also, are you looking for a straight translation of these ships or something that carries the spirit of them forward but modernized (IE: The WWII Iowa or her 90's configuration, or the Yamato as launched, as refitted when she went down, or with a hypothetical refit if she had survived to the 90's like the Iowa)?
In addition, still waiting to hear back for official word if Thunderbolts can be used as torpedoes or not (Because even a sextuplet launch of Mk 48 ADCAP or , which is rare to say the least, should not be represented by a mere SRT-6 rack or the macross missile massacre that is a LRT-20, mass torpedo salvos worked in the pre-guided days but not in more modern environments).
As for getting nuked from orbit. If you have a planet valuable enough to warrant a wet navy for coastal support in the event of invasions, we are talking here about a very high value location... like Terra herself or a major capital world. If the fighting is heavy enough to justify such a massive ship, there has to be the space equivalent of the shore guns... fixed and mobile emplacements capable of keeping the big ships out of bombardment range. Because no one likes trying to support troops moving up the Italian Peninsula and suddenly having half the bloody Alps open up with heavy gauss rifle fire or other such surface to space cannons. Nothing says no to aerospace assets more than a nice heavy fortress that makes you have to come to it. Even a low orbit pass might be enough to deter even a vaunted McKenna after she has had a third of her armor belt shredded and in need of a major repair job, not knowing how many more emplacements are left to be unmasked.
Heck! That might make it a worthwhile campaign all unto itself... trying to push in to knock out a mountain orbital defense instillation or track down a railway... sorry, maglev gun that has been picking off dropships bringing in supplies for weeks.
So yeah, in a situation like that, a good wet navy ship might actually see some fun.
-Edit-
To give an example of what to expect when converting over a pseudo-direct iteration of a gun cruiser might be as follows, a mostly finished thought experiment that needs a bit of polishing up honestly (infact, badly)... but it gives an idea to see if this is what you might be looking for.
Type: Des Moines Class CA
Chassis: Large Naval Vessel (Template D)
Weight: 17,300 tons
Equipment Rating: D
Equipment
Chassis/Controls Armored 4335 tons
Engine: ICE 4590 tons
Cruise: 4
Flank: 6
Fuel: 10,000 km 6885 tons
Armor: (Bar 10) 53.5 tons
Front 80
Front Sides 79/79
Rear Sides 79/79
Rear 80
Main Turrets (3) 77 Each
Secondary Turrets (2) 71 Each
Weapons
Thumper x 3 Turret 1 45 tons
Thumper x 3 Turret 2 45 tons
Thumper x 3 Turret 6 45 tons
Thumper Ammo(540) Body 27 tons
2 AC/5 Turret 3 16 tons
2 AC/5 Turret 5 16 tons
2 AC/5 Front Left 16 tons
2 AC/5 Front Right 16 tons
2 AC/5 Rear Left 16 tons
2 AC/5 Rear Right 16 tons
AC/5 Ammo (720) Body 36 tons
2 LAC/2 Front 8 tons
2 LAC/2 Front 8 tons
2 LAC/2 Rear 8 tons
2 LAC/2 Rear 8 tons
2 LAC/2 Front Right 8 tons
2 LAC/2 Front Right 8 tons
2 LAC/2 Front Left 8 tons
2 LAC/2 Front Left 8 tons
2 LAC/2 Rear Right 8 tons
2 LAC/2 Rear Right 8 tons
2 LAC/2 Rear Left 8 tons
2 LAC/2 Rear Left 8 tons
LAC/2 Ammo (1080) Body 24 tons
MG Array (3 MG) Front Right 2 tons
MG Array (3 MG) Front Left 2 tons
MG Array (3 MG) Rear Right 2 tons
MG Array (3 MG) Rear Left 2 tons
MG Ammo (1200) Body 6 tons
Advanced Fire Control
Equipment of Note: Items of Note: 1 Helipad (stern hex), 2 VTOL Hangar Bays (100 tons), MASH (4 Theaters), Communications Equipment (7 tons), Mess Hall, Liquid Cargo Bay (200 ton fuel capacity), 1 Lift Hoist, 2 Searchlights, 2 Vehicle Bays (50 tons each, 2 doors, 1 right, 1 left), Flag Officer Quarters (5 1st class quarters), Infantry Bay (4 foot platoons), Crew Quarters (160 extra crew quarters), Regular Cargo bay (300 tons)
Total Crew: 133 enlisted, 21 officers, 5 Flag officers
That is one of the larger heavy gun cruisers built (the Prinz Eugen is a wee bit bigger at 18,400 full displacement, Tone at 15400 or so, and a Ticonderoga is a mere 9,600 tons... so a slightly enlarged Sovereign might work for you there... just to give you a sense of what could be done) and it wouldn't take much scaling up to reach the mammoth beasts of the sea.
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