Battlecruiser – fast battleship Haruna

Side armour of the Kongō class ships comprised several dozen, 203 mm armour plates, tightly connected together and bolted to the 16 mm side of the hull. The plates formed an armoured belt stretching from the A barbette of the main battery to the Y barbette. Individual segments of the armour plates were made of KC steel (Krupp Cemmented). The upper part of the main belt was placed directly on the bottom plate. Its thickness was constant at 152 mm. It was made of KC steel and installed directly to the 13 mm side plating made of NS steel (Nickel Steel). A third, 152 mm armoured belt, made of KC steel, was above it, mounted, as the latter one, to the 13 mm NS side plating. The bow section, at the water line, from the A turret to the stem and the stern section from the Y turret to the rudder shaft were covered with thinner, 76 mm armour, made of KC steel. Below the main belt, there was a narrow belt made of 76 mm KC steel, that formed a base for the lower edge of the main belt.
Horizontal armour on decks above the water line did not exist on the Kongō class ships. The sides of the battlecruiser’s hull were protected by three armoured belts placed one above the other. Only the upper deck provided horizontal protection for the ship. Individual segments of the deck were made of 38 mm NS steel plates and covered mainly the edges of the deck between the B and X barbettes, leaving part of the midship in the line of symmetry, unprotected.

Armour below the water line

Vertical protection system of the battlecruiser, below the water line, consisted of armour covering the ammunition magazines of the main artillery turrets. It was made of 12.7 to 19 mm NS steel. Horizontal armour of the decks was slightly better. The first platform deck was armoured in some areas. In the bow section, it was the torpedo room with a roof made of 38 mm NS steel. The bow side bulkhead was made of 127 mm KC steel. The artillery ammunition magazines’ floor was made of 25 mm NS steel, their sides were protected by a 19 mm NS bulkhead. Another ammunition magazine, behind the boiler room, had a 25 mm NS floor. Side bulkheads in that area were of various thickness. On the level of the first platform deck, they were partially made of 19 mm NS steel, a little higher – on the level of the lower deck – they were 12.7 mm thick (NS). The ammunition magazine below the Y turret barbette had identical armour – 25 mm NS floor, 19 mm NS bulkheads. Armour of the under deck (Ge Kanpan) was almost entirely made of 19 mm NS steel. The stern was an exception. The torpedo room was covered with 64 mm KC steel plates, the rudder engine room was protected by a 51 mm NS deck.

Engine room

When the Kongō class battlecruisers entered service, they were equipped with standard propulsion designed for big units, comprising 2 turbines and 36 large boilers supplying heated steam. However, not all ships were fitted with the same turbines and boilers. The first three ships received the Parsons turbines. Haruna was the exception, since she was the only one of the four units to be equipped with the Brown-Curtiss turbines. As far as boilers are concerned, only Hiei was fitted with the I Kanpon boilers while the other battlecruisers were equipped with 36 boilers of the Yarrow type. Detailed data concerning the engine room before refit is presented in Table 3. After being rebuilt, the main changes concerned only boilers (Table 42). The battlecruisers were very manoeuvrable. During turning manoeuvre trials conducted by Haruna with displacement of 35.921 T at 35.92 knots and 29.6 degrees rudder deflection, after 820 m, the battlecruiser’s turning diameter was 953 m with 9.5 degrees heel. Kirishima at the speed of 28.56 knots and  30 degrees rudder deflection, after 871 m, reached a turning diameter of 826 m at 11.5 degrees heel.

Main artillery

In December of 1910, the Prime Minister, M. Saitō, informed the public of plans to build new ships with main armament comprising eight 12-inch guns. Initial scheme of the 1st type battlecruisers: B.39 – B.41 Kongō class is presented in Table 6.