Just what we need - Battleships. The ability to fire a projectile that weighs more than Volkswagen in excess of 30 miles.
oh, in your reading your original post - you mentioned 13-20" shells...
Pray tell, what WW2 battleships had 13" or 20" guns?
14", 15", 16", or 18" - those are your choices.
US Fast Battleships carried 16"/50 cal (Iowa) and 16"/45 (SoDak & Washington)
KGV Class (Prince of Whales, KGV, Anson and Howe were all the same class), 14"/45
Kongo (and her sisters Kirishima, Hiei, and Haruna) 14"/45
Yamato - 18" guns
If you're lucky enough to get a US Battleship, in one single vessel you carry more AA guns than an entire CV group. Add to that the DDs required to protect it, and you have a virtually indestructible wall of ack.
Sorry - nope.
If you want to wish for a useful ship to add to the game, ask for an LST.