 The forward conning tower was protected with heavy armor : the sides were 300 mm thick and the roof was 130 mm ( 5 @.@ 1 in ) thick . The rear conning tower was less well armored ; its sides were only 200 mm ( 7 @.@ 9 in ) thick and the roof was covered with 50 mm ( 2 @.@ 0 in ) of armor plate . The main battery gun turrets were also heavily armored : the turret sides were 270 mm ( 11 in ) thick and the roofs were 110 mm ( 4 @.@ 3 in ) thick . On Hindenburg , the thickness of the turret roofs was increased to 150 mm ( 5 @.@ 9 in ) . The 15 cm guns had 150 mm @-@ worth of armor plating in the casemates ; the guns themselves had 70 mm ( 2 @.@ 8 in ) thick shields to protect their crews from shell splinters . 
