This is a piece of 26" thick armor that was to be used on one of the turrets of the Japanese Yamato-class battleship Shinano. The Shinano was converted to an aircraft carrier before she was completed as a battleship and thus this particular piece was not used. The U.S. Navy got their hands on it after the war and decided to test its strength by firing at point blank with a 16" Mark 7 gun—the same gun used on the Iowa-class battleships.