Port over of a friend's post from the Asia forums.
14.3
Remember this magic number during this thread.
I have myself a Warspite, and tested the Yamato on multiple occasions every now and then.
Now for those who played WoT would know what overmatch is. In WoT, if your shell calibre is more than 3x the thickness if your enemy armor, you will always pen.
In World of Warships, if your shell calibre is more than 14.3x than the enemy's thickness, it will always pen.
However you dont really notice this because of overmatching, usually a shell that size