Like all battleships, the Iowa carried heavy armor protection against shellfire and bombs with significant underwater protection against torpedoes. The Iowa’s armor scheme was modeled on that of the preceding South Dakota class, and designed to give a zone of immunity against fire from 16-inch/45-caliber guns between 18,000 and 30,000 yards (16,000 and 27,000 m) away. The magazines and engine rooms were protected by an armored belt 12.2 inches (310 mm) thick, which sloped to give an effective vertical thickness of 13.5 inches (340 mm). Their armor was not sufficient to protect against guns equivalent to their own 16-inch/50-caliber guns; increasing the armor would have increased weight and reduced speed. Missouri and Wisconsin incorporated the most significant change in armor from the Sout