 The Ise class were the only Japanese battleships to place the powder magazine above the shell magazine as the IJN wished to put as much space as possible between the highly flammable propellant and mine and torpedo detonations . The danger from plunging shells at long distances was not appreciated until the fatal magazine explosions of three British battlecruisers during the 1916 Battle of Jutland graphically demonstrated the point . To further protect the magazines the depth of the double bottom was increased to a total of 3 @.@ 58 metres ( 11 ft 9 in ) underneath the barbettes and magazines . Additionally , the vessels contained 660 watertight compartments to preserve buoyancy in the event of battle damage . In addition to the torpedo bulge added when the ships were modernized , the deck armour over the machinery and magazines was increased to a total thickness of 140 mm . Inside the original skin of the ships , two torpedo bulkheads were also added and the turret roofs were increased to a total of 152 millimetres ( 6 in ) of armour . 
