These weapons were used on most Japanese destroyers built between 1926 and 1945 in both single and twin mounts. The mountings for these guns were a revolutionary design, as the Japanese were the first to use weather and splinter-proof mounts on destroyers. The second batch of these destroyers were also the first to use medium caliber guns with high elevations, giving them a DP function. However, the very slow training speeds and lack of power ramming made these mountings almost useless against the fast-moving aircraft of World War II.

These weapons were of built-up construction, originally three layers (Model No. I) and later two layers (Model No. I2) along with the usual breech ring and breech bush. About 700 guns were manufactured. Surprisingly for this size weapon, these guns fired bag ammunition and used a Welin breech-block.

Gun Characteristics

Designation 12.7 cm/50 (5") 3rd Year Type (Model 1914)
Ship Class Used On Fubuki, Shikinami, Akatsuki, Hatsuharu, Shiratsuyu, Asashio, Kagero, Yugumo and Shimakaze Classes
Date Of Design 1926
Date In Service 1928
Gun Weight 4.18 tons (4,245 kg)
Gun Length oa 255.2 in (6.483 m)
Bore Length 250 in (6.350 m)
Rifling Length 211 in (5.351 m)
Grooves (36) 0.060 in deep x 0.261 in (1.52 mm x 6.63 mm)
Lands 0.175 in (4.45 mm)
Twist Uniform RH 1 in 28
Chamber Volume 976 in3 (16 dm3)
Rate Of Fire 5 to 10 rounds per minute 1
  • ^The Warship 2007 essay "The Japanese Destroyers of the Hatsuharu Class" says that the firing rate was about 4.4 rounds per minute per gun, but that the ammunition supply could provide 10 complete rounds per gun per minute. Other sources listed below support the ammunition supply rate of 10 rounds per minute, but also claim higher firing rates. As the agreed ammunition supply rate is more than twice as fast as the slow firing rate claimed by Warship 2007, then a reasonable conclusion is that the Japanese, who pared the weight of these ships to the bone and beyond, would not have wasted a gram in having a supply capacity that was twice as fast as needed. For that reason, I do not believe that the firing rate given in Warships 2007 to be correct (and it is rather slow for a medium caliber Welin breech gun). For this reason, I continue to believe that the Rate Of Fire figures given in the table above are accurate. This was a bag gun that needed to be lowered to at least +10 degrees to be loaded, so my assumption is that the slow 5 RPM rate would be for AA fire while the 10 RPM rate would be for surface fire.


Type Bag
Projectile Types and Weights Common Type 0 HE: 50.7 lbs. (23.0 kg)
Common Type 1 HE 1a: 50.7 lbs. (23.0 kg)
Common Type 3 IS 2a: 50.7 lbs. (23.0 kg)
Common Type 4 IS: 50.7 lbs. (23.0 kg)
ASW 3a: 46.2 lbs. (20.9 kg)
Illum 4a: 50.7 lbs. (23.0 kg)
New Type Projectile 5a: 61.6 lbs. (27.9 kg)
Bursting Charge Common Type 0 HE: 4.15 lbs. (1.88 kg)
Common Type 1 HE: 4.86 lbs. (2.2 kg)
ASW: 8.78 lbs. (4.0 kg)
New Type Projectile: 4.84 lbs. (2.2 kg)
Projectile Length Common Type 0 HE: 17.2 in (43.7 cm)
Common Type 1 HE: 17.2 in (43.7 cm)
Common Type 3 IS: 17.2 in (43.7 cm)
Common Type 4 IS: 17.2 in (43.7 cm)
ASW: 17.2 in (43.7 cm)
New Type Projectile: 21.6 in (54.9 cm)
Propellant Charge 6a All except ASW: 17.0 lbs. (7.7 kg) 30 DC
Muzzle Velocity Common Rounds: 3,002 fps (915 mps)
ASW: 820 fps (250 mps)
Illum: 2,460 fps (750 mps)
Working Pressure 18.0 tons/in2 (2,840 kg/cm2)
Approximate Barrel Life 550 - 700 Rounds
Ammunition stowage per gun about 150 rounds 7a
  • ^Common Type 1 HE was supplied with time fuzes for AA defense. US Naval Technical Mission to Japan report O-19 says that this round had an effective radius of 20.6 yards (19 m) but this seems to be optimistic.
  • ^IS is my abbreviation for the incendiary shrapnel round (sankaidan) intended for AA use. These were officially listed as Common shells, but were actually incendiary fragmentation rounds.
  • ^The flat-nosed ASW projectile was issued in 1943 following extensive testing. This is listed in US Naval Technical Mission to Japan report O-19 as being able to penetrate a 9.85 in (25 cm) plate of Ducol Steel (roughly equivalent to USN HTS) at a depth of 26 feet (8 meters). However, based upon other errors in this document, I would believe this to be an error in metric to english unit conversion and that the actual performance would more likely be 0.985 in (2.5 cm). Range for this performance is not given.
  • ^Illumination rounds were rated at 680,000 candle power and had a maximum range of 17,000 yards (15,540 m).
  • ^"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 and does not appear to have entered service use. This projectile was boat-tailed, more streamlined at 13crh, had a maximum surface range of 25,180 yards (23,025 m) and a maximum AA Ceiling of 49,260 feet (15,010 m) at 90 degrees elevation.
  • ^The propellant charge was in one bag with a 1.75 oz (50 gm) black powder igniter.
  • ^As built the "Specials" carried about 150 rounds per gun. After the rebuilds following the investigation into the capsizing of the torpedo boat Tomozuru and weather-related damage to other ships in 1935, stowage was reduced to 120 rounds per gun.
  • Fuzes were set by hand on the loading tray.


Range with 50.7 lbs. (23.0 kg) HE
Elevation Range
5 degrees 7,910 yards (7,235 m)
10 degrees 11,140 yards (10,190 m)
20 degrees 15,385 yards (14,068 m)
30 degrees 18,235 yards (16,672 m)
40 degrees 19,980 yards (18,269 m)
45 degrees 20,100 yards (18,380 m)
AA Ceiling @ 75 degrees about 40,000 feet (12,200 m)
Range with 46.2 lbs. (22.0 kg) ASW
Elevation Range
40 degrees 4,700 yards (4,300 m)

Minimum range of ASW shell is given as 875 yards (800 m). Ranges less than this tended to ricochet.

Mount/Turret Data

Designation 1b Twin Mounts
   Fubuki (3): Type A
   Shikinami (3), Akatsuki (3) and Hatsuharu (2): Type B
   Shiratsuyu (2), Asashio (3) and Kagero (3): Type C
   Yugumo (3) and Shimakaze (3): Type D

Single Mounts
  Hatsuharu (1) 2b: Type A
  Shiratsuyu (1): Type B

Weight Single Mounts: 18.4 tons (18.7 mt)
Twin Mounts: 32.0 tons (32.5 mt)
Elevation Twin Mounts 3b
   Type A: - 5 / +40 degrees
   Type B: -5 / +75 degrees
   Type C: -7 / +55 degrees
   Type D: -7 / +75 degrees

Single Mount 4b
   Type A: -7 / +55 degrees
   Type B: -7 / +55 degrees

Elevation Rate 6-12 degrees per second officially, but 24 for single mounts and 27 for twin mounts has been reported
Train about +150 / -150 degrees
Train Rate 4-6 degrees per second
Gun recoil N/A
Loading Angle +5 to +10 degrees (Hand ramming) 5b
  • ^The "Special Type" destroyers are usually split into the Fubuki (first 10), the Shikinami (second 10) and the Akatsuki (last 4) sub-classes. Regarding weaponry, the difference between these sub-classes was that the Fubuki had SP guns, while the Shikinami and the Akatsuki had DP guns.
  • ^The Hatsuharu class originally had their single gun superimposed on the bow as can be seen in the photograph below. Following trials with the first two class members where their stability was found to be poor and the investigation into the capsizing of the torpedo boat Tomozuru, these ships were greatly modified to improve their stability. As part of these changes, the single gun was repositioned on the weather deck directly in front of the stern twin mount. The four other members of the class still under construction were completed to the new arrangement.
  • ^Twin mounts had a crew of 16. There was a pusher shell hoist for each gun and charges were passed by hand. Guns were individually sleeved.
  • ^Single mounts had a crew of 10. There was a pusher shell hoist for each gun and charges were passed by hand.
  • ^Although the loading angle was unimpressive for AA use, it should be noted that +10 degrees was sufficient for most surface actions of World War II.
  • These mountings were well liked but were considered to need strengthening, which may have been the cause of the large amount of dispersion noted.
  • Most surviving destroyers had "X" mount removed during the war in order to fit additional 25 mm AA guns.
  • In addition to being weather and splinter proof, these mountings were also proof against poison gas.

Additional Pictures


"Naval Weapons of World War Two" by John Campbell
"The Japanese Ships of the Pacific War" by The Koku-Fan
"The Japanese Destroyers of the Hatsuharu Class" article by Hans Lengerer in "Warship 2007"
"Japanese Super Destroyers" article by A.J. Watts in "Warships Special 2: Super Destroyers" edited by Antony Preston
"Japanese Warships of World War II" by A.J. Watts
"Destroyers 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"
US Naval Technical Mission to Japan report O-54(N): Japanese Naval Guns
Tony DiGiulian's personal files

Page History

05 March 2008 - Benchmark
19 March 2009 - Added note regarding the repositioning of the mountings on the Hatsuharu class, more thoughts on the ROF, fixed typographical error
01 May 2012 - Added picture page
17 December 2013 - Updated photograph of Ayanami
20 December 2015 - Minor additions to photographs
20 March 2019 - Converted to HTML 5 format, reorganized notes, added note regarding time fuzes on Type 1 HE