 The forward conning tower was protected with heavy armor : the sides were 400 mm ( 16 in ) thick and the roof was 170 mm thick . The rear conning tower was less well armored ; its sides were only 170 mm thick and the roof was covered with 80 mm ( 3 @.@ 1 in ) of armor plate . The main battery gun turrets were also heavily armored : the turret sides were 350 mm thick and the roofs were 200 mm thick . The 15 cm guns had 170 mm thick armor plating on the casemates ; the guns themselves had 80 mm thick shields to protect their crews from shell splinters . 
