Maths no good. Start over. Include (BB-47) Washington. Still only Big 10 (retroactively refit the two Tennessees to have 16 inch guns (which as far as I can tell, was never considered) to make them all 16 inch gun battleships).
Nagato Mutsu Nelson Rodney Colorado Maryland (Washington) West Virginia (Tennessee) (California)
Only way to 12 is if you can convince Kaga and Akagi to no get refit, or count them because they were going to be 16 inch battleship/battlecruisers. (or Tosa and Amagi return, but both designs are more guns than any of the Big Seven)
Maths no good. Start over. Include (BB-47) Washington. Still only Big 10 (retroactively refit the two Tennessees to have 16 inch guns (which as far as I can tell, was never considered) to make them all 16 inch gun battleships).
Nagato Mutsu Nelson Rodney Colorado Maryland (Washington) West Virginia (Tennessee) (California)
Only way to 12 is if you can convince Kaga and Akagi to no get refit, or count them because they were going to be 16 inch battleship/battlecruisers. (or Tosa and Amagi return, but both designs are more guns than any of the Big Seven)
Big5: Tennessee, California, Colorado, Maryland, West Virginia + Big7: Nagato, Mutsu, Nelson, Rodney, Colorado, Maryland, West Virginia = Big12: Tennessee, California, Nagato, Mutsu, Nelson, Rodney, 2 Colorado, 2 Maryland, 2 West Virginia
Updated
I was put into the Big 7.
If you put it together with the Big 5, then it's the Big 12!