Medium Caliber Ordnance Imperial Japanese Navy
The main Japanese naval guns of medium caliber can be summarized with the following units: 8″/50 Type II (203 mm),
8″/50 Type I (203 mm), 6″/60 (152 mm), 6″/50 (152 mm), 5.5″/50 (140 mm).
8″/50 Type II / Type 2 naval guns (203 mm)
The 8″/50 Type II also known as guns of 203 mm were mounted in Furutaka, Aoba, Myoko, Takao, Mogami and Tone Japanese heavy cruiser classes. After modernization, Akagi carrier carried six guns. The Kaga carrier also had these guns.
2 GO (Mark II) guns or Type 2 guns (203 mm)
This type was a evolution of Type I and a 33.8 kg (74.5 lb) powder charge to fire 8 in (203.2 mm) projectiles weighing 125.85 kg (277.5 lb) at a velocity of 835 m/s (2,740 ft/s). Rate of fire varied from four or five rounds per minute firing at low angles diminishing to two or three rounds per minute firing at maximum elevation. These guns had a useful life expectancy of 320 to 400 EFC. Several types of turrets were mounted in the cruisers carrying the same Type 2 guns. However, the different types of turrets showed differences in the elevation limit of the guns. In general, the Types 2 (Mark II) guns replaced the original Mark I guns in type C and D turrets so all Japanese heavy cruisers carried Mark II guns in twin turrets by December 1941.
|Akagi carrier||6 Mark I guns in type A casemates with 25° elevation|
|Aoba||3 type C twin turrets with 40° elevation|
|Ashigara||5 type D twin turrets with 40° elevation|
|Atago||5 type E twin turrets with 70° elevation|
|Chikuma||4 type E twin turrets with 55° elevation|
|Chōkai||5 type E twin turrets with 70° elevation|
|Furutaka||3 type E twin turrets with 55° elevation|
|Haguro||5 type D twin turrets with 40° elevation|
|Kaga carrier||10 Mark I guns in type A casemates with 25° elevation|
|Kako||3 type E twin turrets with 55° elevation|
|Kinugasa||3 type C twin turrets with 40° elevation|
|Kumano||5 type E twin turrets with 55° elevation|
|Maya||5 type E twin turrets with 55° elevation|
|Mikuma||5 type E twin turrets with 55° elevation|
|Mogami||5 type E twin turrets with 55° elevation|
|Myōkō||5 type D twin turrets with 40° elevation|
|Nachi||5 type D twin turrets with 40° elevation|
|Suzuya||5 type E twin turrets with 55° elevation|
|Takao||5 type E twin turrets with 70° elevation|
|Tone||4 type E twin turrets with 55° elevation|
Tone-class: main armament and armor
|Aircraft carried:||6 x floatplanes|
Mogami-class: main armament and armor
|Aircraft carried:||3 × Aichi E13A reconnaissance floatplanes|
Furutaka-class: main armament and armor
|Aircraft carried:||(initial) 1, (final) 2|
Myoko-class: main armament and armor
Aoba-class: main armament and armor
|Aircraft carried:||(initial) 1, (final|
Takao-class: main armament and armor
8″/50 Type I naval guns (155 mm)
8″/50 Type I (Mark) I guns were installed in casemates with a maximum elevation of 25 degrees limiting maximum range to 22 kilometers (14 mi). Aircraft carriers originally had four guns originally mounted in two type B twin turrets with a maximum elevation of 70 degrees. These were transferred to casemates in Kaga in 1934 and simply removed from Akagi in 1936. These guns were initially installed in type A low-angle (25°) single mounts aboard Furutaka-class cruisers, in type C (40°) twin turrets in the Aoba class, and in type D (40°) twin turrets in the Myōkō class. Later they were all replaced by Type 2.
Interestingly, Type I can be visually distinguished from Type II guns by an abrupt step in the chase diameter which was absent on the latter guns. (See Campbell, John (1985). Naval Weapons of World War Two. Naval Institute Press. )
6″/60 naval guns (155 mm)
The 6”/60 155 mm guns had a unique deployment history because they literally rotate between ships. They had a good performance and were initially mounted in tripe turrets aboard the heavy cruiser Mogami. At that time, the Mogami was still considered light cruiser. However, soon these guns were replaced by the 8-inch turrets, and the four ships of the Mogami class were modernised. These four apiece were then move aboard the Yamato and Musashi. However, again later in the war they were replaced by more AA mounts in order to fight the increasing US air power. The light cruiser Oyodo also had these batteries.
6″/50 Naval guns (155 mm)
These guns were mounted in single casemates only in few ships such as Fuso and Kongo battleships. Dual mounts were also installed for the Agano-class light cruisers.
In the 1930s, the Kongō-class battleships were modernized, at which time these guns were replaced by new 12.7 cm/40 DP guns. The old guns were placed in storage and were reused on the Agano light cruisers. Some were taken to Guam and were used for coastal defense batteries.
In the Agano-class cruisers, the gun could elevate to 55 degrees for anti-aircraft fire; however, its manual loading method allowed a rate of fire of only about 6 rounds per minute, which significantly limited its utility as an anti-aircraft weapon.
|Shell||100 pounds (45 kg)|
|Caliber||6-inch (152.4 mm)|
|Elevation||-5 to +30(Kongo & Fuso)
-5 to +55 (Agano)
|Traverse||-70 to +70(Kongo & Fuso)
-150 to +150 (Agano)
|Rate of fire||6 (effective)|
|Muzzle velocity||850 m/s|
|Effective firing range||18,000 meters (Kongo & Fuso)
21,000 meters (Agano)
5.5″/50 naval guns (140 mm)
The 140 mm /50 3rd Year Type naval gun was a Japanese low-angle weapon that started to be operative during World War I. The main versions included 3rd year type and 11th year type. Submarine cruisers used the shorter-barreled 14 cm/40 11th Year Type naval gun. The surface ships that inclided the 3rd year type included the Ise and Nagato-class battleships as single mounts. Several classes of light cruisers suh as Tatsuta, Nagara, Kuma and Naka. For these cruisers the single turret was open in her back for the crew operations. Finally, the light carrier Hosho also had these single turrets.
Tatsuta-class light cruiser armament and armor: