Heavy Cruiser Aoba

Details of the bridge structure. The main gun Type 94 director and the accompanying 6 meter Type 14 rangefinder are mounted at the top. Visualisation 3D: Waldemar Góralski

As originally designed, the cruiser’s main armament was to consist of six main guns mounted in separate “A” Model turrets based on the smaller units housing 14 cm guns on the cruiser Yobari. As has been previously mentioned, Fujimoto was pressured by the Gunreibu to place the ship’s guns in new twin turrets. Engineer Hada  adapted the turret designed earlier for the Myoko class vessels to be used on Aoba class cruisers. The adaptation work was completed in mid 1925 when the ship was still on the slipway, so all the necessary changes could be easily incorporated into the design. Eventually the cruiser was completed with the same number of guns as Furutaka with the six main 20 cm/L50 guns mounted in three twin “C” Model turrets. Two gun turrets were placed along the ship’s centerline in the bow section and were designated No. 1 and 2. No. 3 turret was mounted in the aft section of the ship. Medium HA (anti-aircraft) artillery included four Type 10 12 cm/L45 guns mounted in “B” Model turrets. Similarly to the main guns, the HA gun fit was also changed compared to the original design that was to include older 8 cm Type 3 guns. The HA guns were all mounted amidships and abreast the smoke stacks. Additionally, two Lewis 7.7 mm machine guns were mounted on the bridge structure. The torpedo armament included 12 Type 12 61 cm torpedo tubes grouped in six twin launcher assemblies and firing Type 8 torpedoes.
In November 1938 Aoba was brought to Sasebo shipyard for modernization and reconstruction work. The project was completed on October 30, 1940 and resulted in some changes in the cruiser’s armament fit. The main artillery consisted of six Type 3 20 cm/L50 guns mounted in three twin “C” Model turrets. Medium artillery comprised 4 single Type 10 12 cm/L45 guns placed in single “B2” Model turrets. The ship was also equipped with four twin Type 96 25 mm AA cannons and two sets of twin Type 93 13 mm machine guns. Torpedo armament consisted of two quadruple Type 92 61 cm torpedo tubes protected by a Type 1 armor screen. The ship carried sixteen Type 90 torpedoes that were replaced in 1940 by Type 93 weapons.

The stern installation of triple 25 mm Type 96 (96 Shiki) anti-aircraft guns.  Visualisation 3D: Waldemar Góralski


A. Main 20 cm artillery
The gun was designed in 1924 by Chiyokichi Hada. In 1925 Hada also designed a single gun turret, but it was his 1926 twin gun turret design that was used on Furutaka and Aoba cruisers. Originally the turret was designed for Myoko class cruisers, but Cmdr. Fujimoto incorporated it into Aoba plans following the directives of the Navy General Staff. Cmdr. T. Fukuda was in charge of the weapon’s production at Kure and Mururoan, while Adm. K. Hidaka oversaw the manufacturing of gun turrets at Kure and Yokosuka. The guns were also installed on Amagi and Kaga aircraft carriers. According to the Report 0-47(N)-1 300 20 cm guns and 120 gun turrets were manufactured. The specifics of the weapon can be found in Table 3.

Table 3. 20 cm gun specifications
No.    Parameter    Data
 1    Designation    Type 3
 2    Caliber of bore    20 cm
 3    Actual caliber    20,32 cm (8 in)
 4    Length in calibers    50 cal
 5    Weight with breech    17,800 kg (39,300 lb)
 6    Length of barrel    1,000 cm (393.7 in)
 7    Length overall    1,031 cm (408 in) In early examples semi-wire wound.
 8    Barrel design    Later built-up. After reconstruction built-up with removable sleeve.
 9    Breech mechanism    swinging screw
10    Number of grooves    48 (2,28 mm x 8,299 mm)
11    Length of lead section    848.09 cm (334 in)
12    Length of breech     134.825 cm (53.1 in)
13    Chamber volume    68 l
14    Powder charge    2 bags
15    Muzzle velocity     840 m/sec (common shell)
16    Bore pressure (max)     30 – 31.3 kg/mm2
17    Powder gas pressure    6.1 kg/mm 2
18    AP shell weight     125.85 kg (278 lb)
19    Illumination shell weight     ??
20    Shrapnel shell weight    33.8 kg (75 lb)
21    Fuze weight    0.170 kg
22    Maximum range    28,900 m
23    Maximum firing height    10,000 m
24    Barrel life    320 – 400 rounds

B. 12 cm anti-aircraft (HA) artillery