 The main gun turrets had sides 300 mm thick with 150 mm roofs . The gun ports were protected by 50 mm plates , and 25 mm bulkheads separated each gun . The barbettes were 247 @.@ 5 mm ( 9 @.@ 74 in ) thick , decreasing to 147 @.@ 5 millimetres ( 5 @.@ 81 in ) when behind other armour . They were shaped like truncated cones which matched the trajectories of descending shells and thus lessened their protective value . The conning tower was 400 millimetres ( 15 @.@ 7 in ) thick , reduced to 300 mm below the upper deck . The funnel uptakes were protected by 50 mm of armour . The upper deck was 37 @.@ 5 millimetres ( 1 @.@ 48 in ) thick while the middle deck consisted of 40 @-@ millimetre ( 1 @.@ 6 in ) plates of KNC on 25 mm of nickel @-@ steel over the armoured citadel . Underwater protection was minimal : there was only a 10 @-@ millimetre ( 0 @.@ 39 in ) watertight bulkhead behind the upward extension of the double bottom , and even this was thinner as the hull narrowed towards the end turrets . 
