Medium caliber Ordnance Imperial Japanese Navy


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)

 

Myoko heavy cruiser showing her main guns 203 mm in trials during 1941.

Myoko heavy cruiser showing her main guns 203 mm in trials during 1941.

 

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.

Ship Gun Installation
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

Armament:
  • 8 × 203 mm guns (4 x 2)
  • 8 × 127 mm guns (4 x 2),
  • 12 × 25 mm Type 96 AA guns (6 x 2)
  • 12 × 610 mm torpedo tubes (4 x 3)
Armour:
  • 100 mm (3.9 in) (belt)
  • 65–30 mm (2.6–1.2 in) (deck)
Aircraft carried: 6 x floatplanes

Mogami-class: main armament and armor

 

Armament:
  • (initial)
  • 5 × triple 15.5 cm/60 3rd Year Type guns (replaced by 5 × twin 20.3 cm/50 3rd Year Type 2 guns from 1939)
  • 4 × twin 127 mm (5.0 in) guns
  • 4 × single 40 mm AA guns
  • 4 × triple 610 mm (24 in) torpedo tubes
Armor:
  • Belt: 100 mm (3.9 in) (140 mm (5.5 in) over magazines)
  • Deck: 35 mm (1.4 in)
  • Turrets: 25 mm (0.98 in)
  • Magazines: 127 mm (5.0 in)
Aircraft carried: 3 × Aichi E13A reconnaissance floatplanes

Furutaka-class: main armament and armor

Armament:
  • (initial)
  • 6 × 20 cm (7.9 in)/50-cal Mark I guns (6 × 1)
  • 4 × 76.2 mm (3 in)/40-cal high-angle guns (4 × 1)
  • 12 × 61 cm (24 in) torpedo tubes (6 × 2)
  • (final)
  • 6 × 8 in (203 mm)/50-cal Mark II gun (3 × 2)
  • 4 × 12 cm (4.7 in)/45-cal high-angle guns (4 × 1)
  • 8 × 25 mm (4 × 2) automatic cannon
  • 8 × 61 cm (24 in) Type 93 torpedo tubes (2 × 4)
Armor:
  • Belt: 76 mm (3 in)
  • Magazine: 51 mm (2 in)
  • Turrets: 25.4 mm (1 in)
  • Conning tower: none
  • Decks: 35 mm (1.4 in)
  • Upper Decks: 48 mm (1.9 in)
Aircraft carried: (initial) 1, (final) 2

Myoko-class: main armament and armor

 

Armament:
  • 10 × 20 cm (7.9 in) guns (5×2)
  • 6 × 120 mm (4.7 in) guns (6×1)
  • 12 × 610 mm (24 in) torpedo tubes (4×3)
Aircraft carried: 2

 

Aoba-class: main armament and armor

Armament:
  • (initial)
  • 6 × 20 cm (7.9 in)/50-cal Mark I guns (3 × 2)
  • 4 × 12 cm (4.7 in)/45-cal (4 × 1)
  • 12 × 61 cm (24 in) torpedo tubes (6 × 2)
  • (final)
  • 6 × 8 in (203 mm)/50-cal Mark II guns (3 × 2)
  • 4 × 12 cm (4.7 in)/45-cal (4 × 1)
  • 8 × 25 mm (4 × 2) machine guns
  • 8 × 61 cm (24 in) Type 93 torpedo tubes (2 × 4)
Armor:
  • Belt: 76 mm (3 in)
  • Magazine: 51 mm (2 in)
  • Turrets: 25.4 mm (1 in)
  • Conning tower: none
  • Decks: 35 mm (1.4 in)
  • Upper Decks: 48 mm (1.9 in)
Aircraft carried: (initial) 1, (final

Takao-class: main armament and armor

 

Armament:
  • original layout:
    • 10 × 20 cm/50 3rd Year Type naval guns (5×2)
    • 4 × Type 10 12 cm high angle guns(4×1)
    • 8 × 61 cm torpedo tubes (4×2)
    • 2 × 40 mm AA guns (2×1)
    • 2 x 7.7 mm Type 92 MG (2×1)
  • Final Layout (Takao): 10 × 20 cm/50 3rd Year Type naval guns (5×2)
    • 4 × Type 89 12.7 cm (5 in) dual purpose guns, (4×1)
    • 66 × Type 96 25 mm (1.0 in) AA guns (26×1, 12×2, 24×3)
    • 4 × Type 93 13.2 mm (0.5 in) AA machine guns
    • Type 93 torpedoes (4×4 + 8 reloads)
    • depth charges
  • Final Layout (Maya): 8 × 20 cm/50 3rd Year Type naval guns (4×2)
    • 12 × Type 89 12.7 cm (5 in) dual purpose guns, (6×2)
    • 66 × Type 96 25 mm (1.0 in) AA guns (13×3, 27×1)
    • 36 × Type 93 13.2 mm (0.5 in) AA machine guns
    • Type 93 torpedoes (4×4 + 8 reloads)
    • depth charges
  • Final Layout (Atago): 10 × 20 cm/50 3rd Year Type naval guns (5×2)
    • 8 × Type 89 12.7 cm (5 in) dual purpose guns, (4×2)
    • 60 × Type 96 25 mm (1.0 in) AA guns
    • 4 × Type 93 13.2 mm (0.5 in) AA machine guns
    • Type 93 torpedoes (4×4 + 8 reloads)
    • depth charges
Armor:
  • main belt: 38 to 127 mm
  • main deck: 37 mm (max)
  • upper deck: 12.7 to 25 mm
  • bulkheads: 76 to 100 mm
  • turrets: 25 mm
Aircraft carried:
  • One Aichi E13A1 “Jake”
  • Two F1M2 “Pete” seaplanes

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)

 

Detail of the 15.5 cm/60 3rd Year Type naval gun aboard Yamato.

Detail of the 15.5 cm/60 3rd Year Type naval gun aboard Yamato.

 

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.

Japanese cruiser Oyodo in 1943

Japanese cruiser Oyodo in 1943

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.

Agano twin turrets closeup

Agano twin turrets closeup

 

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.

 

Technical specifications:


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.

 

A lateral view of the IJN cruiser Tatsuta in 1919

A lateral view of the IJN cruiser Tatsuta in 1919. Note the single mount for the 4 × 14 cm/50 3rd Year Type naval guns

 

Tatsuta-class light cruiser armament and armor:

Armament:
  • 4 × 14 cm/50 3rd Year Type naval guns
  • 1 × 8 cm/40 3rd Year Type naval guns
  • 2 × Type 93 13 mm AA machine guns
  • 6 × 533 mm (21.0 in) torpedo tubes 3×2
Armour:
  • Belt: 63 mm (2 in)
  • Deck: 25 mm (1 in)
  • Conning tower: 51 mm (2 in)

 

 


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