 Directly above the main belt , the 15 cm casemate guns were protected with 140 mm ( 5 @.@ 5 in ) thick steel plating . The 15 cm guns in turrets were more exposed and therefore slightly better protected : their side armor was increased to 150 mm ( 5 @.@ 9 in ) , with 70 mm ( 2 @.@ 8 in ) thick gun shields . The 24 cm gun turrets had the heaviest armor aboard ship : 250 mm ( 9 @.@ 8 in ) thick sides and 50 mm thick roofs . The forward conning tower also had 250 mm thick sides , though its roof was only 30 mm ( 1 @.@ 2 in ) thick . The rear conning tower was much less protected . Its sides were only 140 mm thick ; the roof was 30 mm thick . 
