The Type 1 was designed to be used in twin shipboard DP mountings, but this appears not to have made it out of the design stage. Late in the war the project was changed to single land mountings intended for AA defenses around naval bases and then designated as Type 5. Only one Type 5 prototype gun and its mounting were finished before the end of the war. This was found among the debris of the gun mount shop at Kure Navy Yard in December 1945.

Constructed of monobloc autofrettaged barrel (Model No. I3), breech ring and used a semi-automatic horizontal sliding breech mechanism.

Gun Characteristics

Designation 12.7 cm/50 (5") Type 1 (Model 1941)
12.7 cm/50 (5") Type 5 (Model 1945)
Ship Class Used On Type 1: Ships
Type 5: Land
Date Of Design 1941 / 1945
Date In Service 1945 (prototype, only)
Gun Weight 10,284 lbs. (4,665 kg) including breech mechanism
Gun Length oa N/A
Bore Length about 250 in (6.350 m)
Rifling Length N/A
Grooves 36
Lands N/A
Twist Uniform RH 1 in 28
Chamber Volume N/A
Rate Of Fire 13 - 18 rounds per minute


Type Fixed
Weight of Complete Round HE: 105.8 lbs. (48.0 kg)
Projectile Types and Weights HE: 59.5 lbs. (27 kg)
Bursting Charge N/A
Projectile Length N/A
Complete round: 64.2 in (163 cm)
Propellant Charge 21.6 lbs. (9.8 kg)
Muzzle Velocity 2,887 to 2,986 fps (880 to 910 mps)
Working Pressure 17.8 tons/in2 (2,800 kg/cm2)
Approximate Barrel Life N/A
Ammunition stowage per gun N/A

Shells are noted as having long noses, probably 13crh as in other late-war projectiles.


Range with 59.5 lbs. (27 kg) HE
Elevation Range
45 degrees 24,500 to 25,800 yards (22,400 to 23,600 m)
AA Ceiling @ 85 degrees 49,900 to 53,150 feet (15,200 to 16,200 m)

Mount/Turret Data

Designation 1 Ships: Twin Mounting
Land: Single Mounting
Weight 18.6 tons (18.9 mt) without shield
Elevation -8 / +85 degrees
Elevation Rate 18 degrees per second
Train N/A
Train Rate 18 degrees per second
Gun recoil 20.0 in (51 cm) nominal, 20.5 in (52 cm) maximum
Loading Angle Any
  • ^All parameters are for the single land mounting. Many components of this mounting were considered by the USN inspectors to be quite heavy but this was judged to be of little importance for its intended use only on land.


"Naval Weapons of World War Two" by John Campbell
US Naval Technical Mission to Japan report O-47(N)-1: Japanese Naval Guns and Mounts-Article 1, Mounts Under 18"

Page History

21 November 2006 - Benchmark
27 May 2012 - Added sketch
03 January 2021 - Converted to HTML 5 format