10 cm/65 (3.9") Type 98
Updated 27 May 2012

The best Japanese AAA gun of World War II, whose characteristics can only be described as "superb."  Their only fault was a rather short service life, the result of high muzzle velocity and a fast rate of fire.  In 1945, most new production mounts were diverted to shore-based installations.

There were two versions of the gun barrel.  Model Type I used a radially expanded, removable lining while the Model Type I2 was of monobloc construction.  Both types had breech rings and a horizontal sliding breech-block.  Spring-operated, semi-automatic rammers, which were cocked by the recoil force, were mounted above the guns.  These allowed the guns to be loaded at any angle of elevation, an important factor for any AA weapon.  Shells were manually inserted into fuze setting machines before being placed into the loading trays.

A total of 169 guns were completed between 1940 and 1944 with 68 used in land mountings.  All were in twin mounts.

A new 10 cm (3.9") Type 5 (Model 1945) gun was under design at the end of the war, but no guns are known to have been completed.  It was intended that this gun would be a replacement for the 12 cm (4.7") 10th Year Type used on escort vessels.


IJN Hatsuzuki in June 1944
The 10 cm (3.9") guns are in the four main twin mounts
IWM Photograph


I believe this to be Wakatsuki

Gun Characteristics
Designation 10 cm/65 (3.9") Type 98 (Model 1938)
Ship Class Used On Akitsuki, Oyodo, Taiho and B-64 classes
Date Of Design 1938
Date In Service 1942
Gun Weight 6,731 lbs. (3,053 kg)
Gun Length oa 265.0 in (6.730 m)
Bore Length 255.9 in (6.500 m)
Rifling Length 221.7 in (5.631 m)
Grooves (32) 0.49 in deep x 0.219 in (1.25 mm x 5.565 mm)
Lands 0.167 in (4.252 mm)
Twist Uniform RH 1 in 28
Chamber Volume 641 in3 (10.5 dm3)
Rate Of Fire 15 - 21 rounds per minute
Type Fixed
Weight of Complete Round HE - 61.7 lbs. (28 kg)
Projectile Types and Weights HE - 28.67 lbs. (13 kg)
Bursting Charge 2.1 lbs. (0.95 kg)
Projectile Length 16.1 in (41 cm)
Complete Round:  44 in (111.8 cm)
Propellant Charge 13.2 lbs. (6 kg) 30 DC (?)
Cartridge - 33 lbs. (15 kg)
Muzzle Velocity 3,281 fps (1,000 mps)
Working Pressure 19.4 tons/in2 (3,050 kg/cm2)
Approximate Barrel Life 350 - 400 rounds
Ammunition stowage per gun about 400 rounds on larger ships
Oyodo:  200 rounds
Akitsuki:  N/A
Note:  It is interesting to note that the Japanese apparently never developed incendiary shrapnel, ASW or even illumination rounds for this weapon, implying that it was solely intended for use as an AA gun.  Practice shells were provided.
Elevation With 28.67 lbs. (13 kg) HE Shell
Range @ 45 degrees 21,325 yards (19,500 m)
AA Ceiling @ 90 degrees 42,651 feet (13,000 m)
Note:  Effective surface range is given as 15,310 yards (14,000 m) and effective AA range as 12,030 yards (11,000 m).
Mount / Turret Data
Designation Twin Mounts
   Akitsuki (4), Oyodo (4), Taiho (6) and B-64 (8):  Model A
Weight  76,060 lbs. (34,500 kg)
Elevation -10 / +90 degrees 
Elevation Rate 16 degrees per second
Train Oyodo, Taiho and B-64:  About +/-70 degrees 

Akitsuki:  -150 / +150 degrees

Train Rate 11 - 16 degrees per second
Gun recoil Minimum 16.1 in, nominal 19.3 in, maximum 19.7 in
(41 cm, 49 cm and 50 cm)
Loading Angle Any

1) Gun crew in twin mount was about 11 men.

2) Mountings used electro-hydraulic power.  Power was supplied by a 15 hp electric motor operating from 220 Vdc and which ran at 600 rpm.

3) Akizuki class used two dredger hoists to supply ammunition to the working chamber.  From here, rounds were manhandled to loading positions for pusher hoists, one for each gun.  At the top of the hoists, rounds automatically rolled to waiting positions where shell passers handed them to loaders standing on the gun platform, which moved with the guns.  Fuze-setting machines were attached to the breech faces of the guns.  Loading trays were manually operated.

4) The Oyodo class used four bucket hoists which delivered ammunition from the magazines to a working chamber abaft the No. 2 15.5 cm (6.1") gun barbette.  The maximum rate of supply was 20 to 22 shells per minute per hoist.  The ammunition was then carried by hand to the 10 cm (3.9") gun mounts, which were 77 and 135 feet (22 and 41 m) further aft.  There were ready-use ammunition storage lockers near the weapon mountings which allowed for a higher rate of fire for a period of time.  The fuze setting on this class was done by a separate machine before the shells were loaded into the gun.

5) Ramming was via a spring-powered mechanism that was cocked by the recoil force when the gun fired.  The mechanism had a removable pulley arrangement where the gun was depressed to cock the rammer for the first round.  A misfire meant that the subsequent round needed to be rammed by hand, unless there was time to reattach the pulley and cycle the gun elevation.  The rammer was similar to that in the earlier 12.7 cm/40 Type 89, but embodied some improvements, mainly in the tripper gear which had an improved type of tumbler release mechanism.  Early production rammers suffered frequent failures due to fracturing of the rammer heads, but this problem was overcome and they gave good service during most of the war.

6) Distance between gun axes was 26.0 inches (66 cm).

Data from
"Japanese Warships of World War II" by A.J. Watts
"Naval Weapons of World War Two" by John Campbell
"Japanese Cruisers of the Pacific War" by Eric Lacroix and Linton Wells II
"Battleships:  Axis and Neutral Battleships in World War II" by W.H. Garzke, Jr. and R.O. Dulin, Jr.
"The Japanese Ships of the Pacific War" by The Koku-Fan
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"
Page History

26 August 2007 - Benchmark
26 December 2011 - Added information about the 10 cm Type 5
27 May 2012 - Updated to latest template