Battleships are not obsolete.

World War 2 era battleships are obsolete. They are designed to neutralize other warships as well as neutralize near shore threats.

Neutralizing other warships is now done with missles and torpedos. Guns are not needed.

Neutralizing near shore threats can also be done with missles, but it is expensive, compared to shells and gunpowder.

Additionally, if you need to be generous in your ordnance gifts to your enemies, you can easily deplete your missile inventory.

What is needed is a battleship designed specifically to address near shore threats, but with a longer range than a standard 16 inch gun.

We know that extending the range of an artillery piece can be done by simply extending the barrel length. This was demonstrated by a low budget preliminary project in the early sixties, called Project Harp:

https://en.m.wikipedia.org/wiki/Project_HARP

The range of a standard 16 inch naval gun is about twenty miles.

If an extra long range battleship was designed with guns specifically for long range, it seems conceivable a range of 100 miles or more could be achieved.

We have the metallurgy and gunnery expertise to design guns for longer range, possibly in even greater diameters.

An extra long range battleship would be a useful tool to deal with the occasional near shore threats.

If we had such a weapon during the Vietnam War, it is conceivable that we could have sorted Vietnam without losing a single man.

Vietnam is essentially a strip of land running along the coast. An extra long range battleship would have been able to target all the tender bits.

We could have let a very well supplied and trained South Vietnam Army fight their brethren in the North and kept our men off the battlefield.

When the South Vietnam Army identified a target, the USA Navy could have obliterated it, from a safe distance.

And offensives by the North could have been responded to by giving their tender bits a good massage.

That is just a hypothetical example of why an extra long range battleship can occasionally come in handy. We should have a few on hand for random exigencies.

Please note: I have not served in the military nor am I a military expert. I may not have used standard military terminology and I hope that my meaning is understood and does not offend anyone.