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.
Two mountings were removed from Natsuzuki at the end of the war and sent to the USA for examination.
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.
Destroyer Hatsuzuki in June 1944
10 cm (3.9") guns captured by Australian
forces at Balikpapan, Borneo
Side view of above mounting
Breech view of above mounting
|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|
|Note: Akitsuki crewmen reported that 19 rounds per minute was very difficult to acheive and that 15 was more typical.|
|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
|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).|
Akitsuki (4): Model A
Oyodo (4): Model A1
Taiho (6): Model A2
Shinano (8) and B-64 (8): Model A3
|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
Akitsuki: -150 / +150 degrees
|Train Rate||11 - 16 degrees per second|
|Gun recoil||Minimum 16.1 in, nominal 19.3 in, maximum
(41 cm, 49 cm and 50 cm)
1) Model A1 was an open mounting and was used for at least some land mountings. 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).
26 August 2007 - Benchmark
26 December 2011 - Added information about the 10 cm Type 5
27 May 2012 - Updated to latest template
09 August 2014 - Added comment about mountings from Natsuzuki being sent to USA
27 August 2015 - Added photographs of land emplacement
27 September 2015 - Added mounting designations