 When the gun turrets from the World War I @-@ era battlecruisers were modernised , their KCA faceplates were replaced by new ones 13 inches thick , and their roofs were replaced by 6 @-@ inch ( 152 mm ) non @-@ cemented armour plates . Their sides remained 7 – 9 inches ( 180 – 230 mm ) in thickness . The barbettes for the 15 @-@ inch guns were 13 inches thick on the sides , but tapered to 11 – 12 inches ( 279 – 305 mm ) closer to the centreline of the ship . The side and roof armour of the 5 @.@ 25 @-@ inch turrets was 2 @.@ 5 inches ( 64 mm ) thick . Their ammunition hoists were protected by armour 2 – 6 inches ( 51 – 152 mm ) thick . 
