Question: difference between south dakota class and iowa class

title: Iowa-class battleship
text: The Iowas had heavily protected main battery turrets , with the turret face armor of 19.5 inches ( 495 mm ) combination of Class B and STS and turret sides of 9.5 inches ( 241 mm ) Class A and turret rear of 12 inches ( 305 mm ) Class A . The conning tower and the turret barbettes armor is up to 17.3 inches ( 439 mm ) thick Class A and Class B respectively . The propulsion shafts and steering gear had considerable protection , with a 13.5 - inch ( 340 mm ) Class A side strake behind the citadel .