 The ships ' armor scheme was only slightly modified from the Mogami @-@ class cruisers . Their waterline armoured belt extended all the way down to the double bottom . It extended from the forward to the rear magazines below the fore and aft turrets and was angled inwards at the top 20 ° from the vertical to improve its resistance to horizontal shellfire . Over the machinery spaces , it was 100 millimeters ( 3 @.@ 9 in ) thick at the top and tapered to 30 millimeters ( 1 @.@ 2 in ) at the bottom . The outer ends of the fore and aft machinery compartments was protected by a 105 @-@ millimeter ( 4 @.@ 1 in ) transverse bulkhead . On the sides of the magazines , the belt was 140 millimeters ( 5 @.@ 5 in ) thick and tapered to 30 mm at the bottom . The magazines were protected by fore and aft transverse bulkheads 95 – 140 millimeters ( 3 @.@ 7 – 5 @.@ 5 in ) thick . The steering gear and the rudder compartments had sides that consisted of 100 @-@ millimeter ( 3 @.@ 9 in ) plates and their ends were protected by 50 millimeters ( 2 @.@ 0 in ) of armor . 
