Originally published at: Amphisbaena | The Eldraeverse
Amphisbaena-class battleship “Half ahe… that way.” – Capt. Olavi Corel, first captain of Amphisbaena Displacement: 125,000 long tons Length: 330 m (at waterline: 316 m)Beam: 84 m (at waterline: 48 m)Draft: 12.1 m Propulsion: 4 x Empire Nucleonics, ICC 64 MW “Fat Salamander” fission reactors8 x Blackstone Industries, ICC steam turbines and reduction plantIn-house magnetohydrodynamic “inchworm” drive system Speed: 42 knots (non-sustainable emergency power: 48 knots)Range: Unlimited; 12 year refueling interval Complement: 1,672 officers and menThinking Machines, ICC “Admiral Aliniv” Command Optimization Thinker Sensors: Artifice Armaments, ICC, ASR-24/3 air search radarArtifice Armaments, ICC, SSR-36 surface search radarArtifice Shadow Works X-449…
…damn it.
I now have to get out my copy of GURPS Vehicle Builder and build Siren Yamoto, because why not?
(Siren Yamoto is what happens when you say “okay, take the TL-6 warship and build it exactly the same mass with TL-10 technology.” Nine 23cm very long-barreled railguns are going to make anybody’s day unhappy. And AA guns that are actually worth something!)
A Battleship can survive shells piercing their belt armor, a projectile penetrating the turret face results in a dramatic loss of firepower and possibly an explosion, less likely with railguns mind but losing half your firepower to a single shot early in the battle could easily change the course of the engagement. The point being that the turrets ought to be the most armored part of the ship. Further my suspicion is that a conventional 22" gun might be able to pierce the main battery turrets but fail on the belt for at least a little bit.
Lastly super/hyper sonic chaff above the waterline can still deal considerable damage to the target ship even if the main warhead is dust on the wind. Which is to say even if your CIWS is lethally effective you should still intercept weapons over there rather than over here. Which in the context of naval weapons means extended range surface to air missiles because the horizon limits the maximum range of laser weapons even if they are arbitrarily powerful, radar and therefore guns reach a bit further.
Technically the range is limited by consumables carried onboard or about 4.5 million miles.
You also need about twice as much power to go 48 knots verses 42
On the armor, it was mainly the explosion risk I was thinking of; while it does impair firepower, a hit on a railgun turret doesn’t get you a magazine explosion because there’s nothing to explode. The not-immediately-required shells for the conventional guns and especially all those lovely missiles, that’s the kind of thing they want to keep safe behind the extra-heavy citadel armor because a hit on those magazines is uncomfortably likely to be a ship-killer.
On the chaff issue - the CIWS is intended to clean up anything that gets through the screen, and a battleship’s not supposed to operate without screen. Which is to say, there are plenty of those anti-air missiles, but they’re on their equivalent of Aegis cruisers.
I listed the range the same way you tend to see it for CVNs: unlimited in the sense of “you will never run into this issue”. 
I’ll double-check my envelope for the speed, but there is a lot more power available in that mode; “emergency power” is intended to cut off all other power-intensive systems on the ship (railguns, for a start) and dump all of the resulting surplus into the MHD. (The limiter on how long you can get away with that being when the superconducting coils in the MHD quench and vaporize themselves because you’ve spent too long playing chicken with the critical field/current.)
Ooh, that’s an interesting-looking piece of software.
/me downloads