Development of the Imperial Japanese Navy Battle Cruiser (Part 1)

Taisho 9, (1920)
The British navy promoted the construction plan of the battle cruiser which 19cm gun carries. However, the imperial navy(Japanese navy)had already ended the design of the battle cruiser of 20cm gun.

October of the same year, Mr.Hiraga of the design chief of navy shipbuilding-official, he discovered that a high-speed ship could be built by improving the llength/ breadth ratio of a hull. And started the 7,600t type design of 'Furutaka' 'Aoba' 'Kinugasa' of a new style battle cruiser.

The six main guns have been arranged on the central line of a hull.. This is the first model at the battle cruiser in the world. Two sets of guns have been saved compared with arrangement of the conventional main guns.

But, the power of bombardment was the same as that of 8 sets of the main guns.
And carries out various improvements and 'Furutaka' class enlarged the of the length/breadth ratio of a hull with 11.4.

The conventional battle cruiser was 8.7 to 10 of the length/breadth ratio.

'Kuma' is10.7.'
'Yubari' was the ratio of 11.
(This cruiser is the design of Mr.Hiraga and is the experiment warship of a high-speed warship.)

The 'Furutaka' class exceeds this, and it became the most smart hull in the battle cruiser in the world.
However, when a hull is made long and slender, much more longitudinal strength of a hull is needed.
For this reason, improvement for the high speed was not able to do the battle cruiser in the world

However, The imperial navy had already solved this problem.
As the method of reinforcing hull strength, it is the structure of sharing the strength of a hull with some defense armor.

This method is adopted by battle cruiser 'Yubari'.
(The conventional armor was attached in the outside of side shell. Therefore, armor was able to remov.

However, Mr.Hiraga, armor was made into the structure which constitutes a hull.
Therefore, removal of armor cannot do after construction.)

The length of 'Yubari' is 140m. 'Furutaka' has 180m length, this method is insufficient for securing strength of a hull.
But, Furthermore, 'Mr.Hiraga' adopts an epoch-making method.