The Ise @-@ class ships ' waterline protective belt had a maximum thickness of 299 mm ( 11 @.@ 8 in ) of Vickers cemented armour amidships ; below it was a strake of 100 mm ( 3 @.@ 9 in ) armour . The upper armoured deck consisted of two layers of high @-@ tensile steel 55 mm ( 2 @.@ 2 in ) thick and the lower armoured deck also consisted of two layers of high @-@ tensile steel , but only 30 mm ( 1 @.@ 2 in ) thick . The sides of this deck sloped downwards to meet the bottom of the lower strake of the belt armour . The ends of the belt armour were closed off by bulkheads that ranged in thickness from 203 to 102 mm ( 8 to 4 in ) . The turrets were protected with an armour thickness of 254 mm ( 10 in ) on the face and 76 mm on the roof . The casemate armour was 149 mm ( 5 @.@ 9 in ) thick and that of the barbettes was 299 mm thick rather than the originally planned 305 mm . The sides of the conning tower were 305 mm thick .