This was an AAA weapon derived from the single-purpose 12 cm/45 (4.7") 3rd Year Type. Most cruisers built in the 1920s and early 1930s were armed with this gun for their secondary batteries. During World War II it was used in coastal batteries and still used afloat on unreconstructed cruisers and on many escort and auxiliary ships as well as the carrier Akagi. Considered to be very reliable weapons.
The four Myôkô class cruisers conducted AA trials with these guns in 1931. Steaming at 18 knots and using the the Type 89 HA computer, the cruisers scored 2.2% hits against aerial targets towed at 60 to 70 knots at altitudes of 1,500 to 2,000 m (4,900 to 6,600 feet). Firing was at an average of 6.4 rounds per minute at ranges between 2,000 and 5,500 m (2,200 and 6,000 yards).
The carrier Kaga and those cruisers modernized during the late 1930s had these weapons replaced by the 12.7 cm/40 (5") Type 89 AA gun. However, Akagi carried them to her end at Midway.
The earlier guns were of built-up construction but the later ones were of monobloc construction. All used a semi-automatic sliding breech-block mechanism. A total of about 3,000 guns were manufactured, with 2,320 (one source says 2,152) of them being produced b etween 1942 to 1945.
|Designation||12 cm/45 (4.7") 10th Year Type (Model 1921)|
|Ship Class Used On||Originally: Most cruisers
World War II: Akagi, Taiyo, Unyo, Kako, Aoba, Myôkô, Chokai, Maya, Yubari, Ioshima classes as well as many smaller escort and auxiliary vessels
|Date Of Design||1921|
|Date In Service||1926|
|Gun Weight||2.9 tons (2.95 mt)|
|Gun Length oa||220.6 in (5.604 m)|
|Bore Length||212.6 in (5.400 m)|
|Rifling Length||183 in (4.649 m)|
|Grooves 1||(34) 0.057 in deep x 0.263 in (1.45 mm x 6.688 mm)|
|Lands||0.173 in (4.40 mm)|
|Twist||Uniform RH 1 in 28|
|Chamber Volume||657.5 in3 (10.774 dm3)|
|Rate Of Fire||10 - 11 rounds per minute maximum
6 - 8 rounds per minute effective
1 Some guns had 36 instead of 34 grooves.
|Weight of Complete Round||Common Type 0 HE: 75 lbs. (34 kg)
Common Type 1 HE: 75 lbs. (34 kg)
|Projectile Types and Weights||Common Type 0 HE: 44.9 lbs. (20.3 kg)
Common Type 1 HE: 44.9 lbs. (20.3 kg)
Common Type 4 IS 1: N/A
ASW 2: 36.3 lbs. (16.4 kg)
Illum 3: about 44.9 lbs. (20.3 kg)
New Type Projectile 4: 49.6 lbs. (22.5 kg)
|Bursting Charge||Common Type 0 HE: 3.75 lbs. (1.7 kg)
Common Type 1 HE: 4.07 lbs. (1.9 kg)
ASW: 7.19 lbs. (3.8 kg)
New Type Projectile: 4.07 lbs. (1.9 kg)
|Projectile Length||Common Type 0 HE: 16.0 in (40.8 cm)
Common Type 1 HE: 16.0 in (40.8 cm)
ASW: 16.4 in (41.5 cm)
New Type Projectile: 20.3 in (51.6 cm)
Complete Common HE Rounds: 37.0 in (94 cm)
|Propellant Charge||Common charge (prior to 1929): 11.2 lbs. (5.06 kg) 36 C2
Common charge (after 1929): 12.1 lbs. (5.5 kg) 30 DC
Reduced charge: [Weight N/A] 36 C2 or 30 DC or 20 T2
Light charge: [Weight N/A] 20 C2 or 20 C3
Cartridge: 30 lbs. (14.4 kg)
|Muzzle Velocity 5||Common HE: 2,707 to 2,723 fps (825 to 830 mps)
Illum: 2,297 fps (700 fps)
ASW: 820 fps (250 mps)
|Working Pressure||16.8 tons/in2 (2,650 kg/cm2)|
|Approximate Barrel Life||700 - 1,000 rounds|
|Ammunition stowage per gun||200 - 250 rounds|
1 IS is my abbreviation for the incendiary shrapnel round (sankaidan) intended for AA use.
2 The flat-nosed ASW projectile was issued in 1943 following extensive testing.
3 Illumination rounds were rated at 600,000 candle power and had a maximum range of 15,310 yards (14,000 m).
4 "New Type Projectile\" is the designation used in the US Naval Technical Mission to Japan report O-19. This projectile was under development at the end of the war with production just beginning and may have entered actual service use. This projectile was boat-tailed, more streamlined at 13crh, had a maximum surface range of 22,430 yards (20,500 m) and a maximum AA Ceiling of 42,660 feet (13,000 m) at 75 degrees elevation.
5 A serious fault of this weapon was that the propellant did not totally combust before the projectile left the muzzle, leading to irregular muzzle velocities. Late in the war, a tubular grain charge was introduced which gave much more regular performance without increasing the working pressure or muzzle velocity.
|45 degrees||17,500 yards (16,000 m)|
|75 degrees||32,800 feet (10,000 m)|
|40 degrees||4,375 yards (4,000 m)|
Minimum range of ASW shell is given as 750 yards (820 m). Ranges less than this tended to ricochet.
|Elevation||-10 / +75 degrees|
|Elevation Rate||B: Manually operated, only
B2 and A2: 6.5 degrees per second
C: N/A (probably 6.5 degrees per second)
|Train||Larger ships: About +/- 70 degrees|
|Train Rate||B: Manually operated, only
B2 and A2: 10 degrees per second
C: N/A (probably 10 degrees per second)
1 Information about the Type C mounts in this table is the result of analyzing data presented in the sources below.
2 The Aoba and Myôkô classes were refitted with B2 mounts during the early 1930s.
3 C, B2 and A2 mounts were electro-hydraulically powered.
4 This twin mount was also used on auxiliary ships.
"Naval Weapons of World War Two" by John Campbell
"Japanese Cruisers of the Pacific War" by Eric Lacroix and Linton Wells II
"Anatomy of the Ship: The Heavy Cruiser Takao" by Janusz Skulksi
"Japanese Warships of World War II" by A.J. Watts
"Cruisers of World War Two" by M.J. Whitley
US Naval Technical Mission to Japan report O-19: Japanese Projectiles General Types
US Naval Technical Mission to Japan report O-47(N)-1: Japanese Naval Guns and Mounts-Article 1, Mounts Under 18"