26-inch thick armor from Japanese Yamato class battleship, pierced by a US Navy 16-inch gun firing a .50 caliber shell.
That is impressive.
Beat you by 16 seconds
I’ve seen that piece of Yamato armor numerous times. It wasn’t struck by 16” Superheavy AP fired from a 50 caliber Iowa class rifle, it was struck by a standard 16” AP fired from a 45 caliber Washington/South Dakota class rifle.
The important thing in looking at the damage to that plate isn’t the full penetration — it’s the massive spalling and cracking around the penetration. Turns out Yamato-type armor was pretty brittle and the plate was shattered by the hit.