Submarines aren’t much good for naval bombardments. Or boarding captured vessels. And when they’re “undetectable [mostly],” they also have limited radio comms, which means limited capacity to respond to changes in orders.
Yup. Submarines are for NUCLEAR war.
Battleships are for CONVENTIONAL war.
I think it would be cool to have 4 of them operating just for camel-jockey wars going on. But their range is limited to about 30 miles of shore bombardment. B52s, smartbombs, laser-guided missiles, A10s and AC130 Ghostriders have that beat. Just do a cost analysis to see which ones work better for the intended purposes.