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 between 1942 to 1945.
12 cm/45 (4.7") guns on Heavy Cruiser IJN
12 cm/45 (4.7") gun captured on hill east
of the Orote Peninsula Airfield, Guam
Breech of above weapon
|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)|
|(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
|Note: 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)
Others - N/A
|Projectile Types and Weights
(see Note 1)
|Common Type 0 HE - 44.9 lbs. (20.3 kg)
Common Type 1 HE - 44.9 lbs. (20.3 kg)
Common Type 4 IS - N/A
ASW - 36.3 lbs. (16.4 kg)
Illum - about 44.9 lbs. (20.3 kg)
New Type Projectile - 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||Common HE - 2,707 to 2,723 fps (825 to
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) 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.
3) The flat-nosed ASW projectile was issued in 1943 following extensive testing.
4) Illumination rounds were rated at 600,000 candle power and had a maximum range of 15,310 yards (14,000 m).
5) "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.
|Elevation||With 45.0 lbs. (20.4 kg) HE Shell and 30 DC propellant|
|Range @ 45 degrees||17,500 yards (16,000 m)|
|AA Ceiling @ 75 degrees||32,800 feet (10,000 m)|
|Elevation||With 36.3 lbs. (16.4 kg) ASW Shell|
|Range @ 40 degrees||4,375 yards (4,000 m)|
|Note: Minimum range of ASW shell is given as 750 yards (820 m). Ranges less than this tended to ricochet.|
Aoba (4), Myôkô (6), Yaeyama (2) and Shirataka (3): B
Furutaka (4), Takao (4), Taiyo (4) and "improved Taiyo" (8): B2
Mikura (Type B escort) (3), Ukuru (Modified Type B escort) (3), Kaikoban I (Type C escort) (2) and Kaikoban II (Type D escort) (2): C
B: 7.7 tons (7.8 mt)
B2: 9.8 tons (10.0 mt)
|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) The Aoba and Myôkô classes were refitted with B2 mounts during the early 1930s.
2) C, B2 and A2 mounts were electro-hydraulically powered.
3) Information about the Type C mounting is a result of my deductions from data presented in the sources below.
28 December 2008 - Benchmark
25 December 2011 - Added information about cruiser and escort mountings
21 July 2015 - Added propellant information