of the belt armour. The ends of the belt armour were closed off by bulkheads that ranged in thickness from . The turrets were protected with an armour thickness of on the face and 76 mm on the roof. The casemate armour was 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. 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 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 of armour. Fire control and sensors While the details of the ships' fire-control instruments are not fully available, it is known that the ships were fitted with a fire-control director after completion. No computer was fitted at that time and data from the rangefinders had to be processed manually. Turrets 2, 3, and 5 were built with imported Bausch & Lomb rangefinders. These were felt to be inferior to the British Barr & Stroud instruments used on other ships and were removed in 1920. They were replaced by either the British rangefinders or domestically built instruments of length. In the late 1920s the fire-control systems were upgraded and additional platforms were added to the foremast to accommodate them. A pair of directors for the 12.7 cm AA guns were added, one on each side of the forward superstructure, in the early 1930s. The fire-control systems were again upgraded in the mid-1930s and directors were added for the 25 mm AA guns. Both ships had rangefinders installed at the top of the pagoda