![](https://i.redd.it/ec01otqc80e11.jpg)
This armor was on the front of the Yamato class 18.1 inch gun turret. The hull armor itself was around 16 inches. This particular piece was likely left over from the Shinano after she was converted to a Carrier. And was likely used as a test against our battleships 16 inch guns. However I don't know anything about the parameters of the test such as range or trajectory.