 New Jersey 's main armored belt was 11 in ( 279 mm ) thick over the magazines and the machinery spaces and 6 in ( 152 mm ) elsewhere . The main battery gun turrets ( and the secondary turrets on top of them ) had 12 @-@ inch ( 300 mm ) thick faces , and the supporting barbettes had the 10 in ( 250 mm ) of armor plating . The conning tower had 9 in ( 230 mm ) thick sides . 
