The M6A3 was capable of penetrating of armor plate. These are the motivations for new types of armor plate. The deck was covered with thick armor plate. Welding gradually replaced riveting and bolting as a means of fastening rolled armor plate together. Casemated guns mounted in the hull had between of armor plate. The ship was protected with Krupp cemented armor plate. Her conning tower was covered with of armor plate on the sides. At , the Mk. 8 could penetrate of vertical steel armor plate. The development of high-explosive shells made the use of iron armor plate on warships necessary. It was like the armor plate of a battleship being pierced. This tough steel alloy was originally developed for the steel armor plate of battleships. Each armor plate is laboratory tested and certified. The Model S has aluminum-alloy armor plate. The sides of the M36's rounded turret were thick, constructed of rolled armor plate. The Mark 37 director aboard is protected with of armor plate and weighs 16 tons.