Japan
12.7 cm/50 (5") 3rd Year Type
Updated 05 March 2008
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 brush.  About 700 guns were manufactured.  Surprisingly for this size weapon, these guns fired bag ammunition and used a Welin breech-block.
WNJAP_5-50_3ns_Sagiri_pic.jpg

IJN Sagiri
This was one of the first destroyers to carry the DP version of the 12.7 cm (5") gun
"20" is the division number, all destroyers in that division carried this number
WNJAP_5-50_3ns_Ikazuchi_pic.jpg

IJN Ikazuchi off the Chinese coast in 1938
U.S. Naval Historical Photograph # NH 74173
WNJAP_5-50_3ns_Ayanami_pic.jpg

Stern of IJN Ayanami
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Gun Characteristics
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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
(see Note)		 5 to 10 rounds per minute
Note:  "The Japanese Destroyers of the Hatsuharu Class" says that the firing rate was about 4.4 rounds per minute per gun, but that each ammunition supply hoists could provide 10 complete rounds per minute (there were two hoists in twin mounts and one in single mounts).  As this was roughly twice as fast as the firing rate, this value does not seem to be accurate, hence my continued use of the above figures which come from the other sources listed below.
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Ammunition
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Type Bag
Projectile Types and Weights
(see Notes 1 and 4)		 Common Type 0 HE - 50.7 lbs. (23.0 kg)
Common Type 1 HE - 50.7 lbs. (23.0 kg)
Common Type 3 IS - 50.7 lbs. (23.0 kg)
Common Type 4 IS - 50.7 lbs. (23.0 kg)
ASW - 46.2 lbs. (20.9 kg)
Illum - 50.7 lbs. (23.0 kg)
New Type Projectile - 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 All except ASW - 17.0 lbs. (7.7 kg) 30 DC
ASW - N/A
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
(see Note 7)		 about 150 rounds
Notes: 

1) 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.

2) The propellant charge was in one bag with a 1.75 oz (50 gm) black powder igniter.

3) Fuzes were set by hand on the loading tray.

4) "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.

5) 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.

6) Illumination rounds were rated at 680,000 candle power and had a maximum range of 17,000 yards (15,540 m).

7) As built the "Specials" carried about 150 rounds per gun.  After the rebuilds following the Tomodzuru capsizing and weather-related damage in 1935, stowage was reduced to 120 rounds per gun.
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Range
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Elevation With 50.7 lbs. (23.0 kg) HE Shell
Range @ 5 degrees 7,910 yards (7,235 m)
Range @ 10 degrees 11,140 yards (10,190 m)
Range @ 20 degrees 15,385 yards (14,068 m)
Range @ 30 degrees 18,235 yards (16,672 m)
Range @ 40 degrees 19,980 yards (18,269 m)
Range @ 45 degrees 20,100 yards (18,380 m)
AA Ceiling @ 75 degrees about 40,000 feet (12,200 m)
Elevation With 46.2 lbs. (22.0 kg) ASW Shell
Range @ 40 degrees 4,700 yards (4,300 m)
Note:  Minimum range of ASW shell is given as 875 yards (800 m).  Ranges less than this tended to ricochet.
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Mount / Turret Data
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Designation
(see Note 4)		 Twin Mounts
   Fubuki (3):  Type A
   Shikinami (3), Akatsuki (3) and Hatsuharui (2):  Type B 
   Shiratsuyu (2), Asashio (3) and Kagero (3):  Type C
   Yugumo (3) and Shimakaze (3):  Type D

Single Mounts
   Hatsuharu (1):  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
   Type A:  - 5 / +40 degrees
   Type B:  -5 / +75 degrees
   Type C:  -7 / +55 degrees 
   Type D:  -7 / +75 degrees

Single Mounts
   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
(see Note 7)		 +5 to +10 degrees (Hand ramming)
Notes:

1) These mountings were well liked but were considered to need strengthening, which may have been the cause of the large amount of dispersion noted.

2) Most surviving destroyers had "X" mount removed during the war in order to fit additional 25 mm AA guns.

3) In addition to being weather and splinter proof, these mountings were also proof against poison gas.

4) 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.

5) Twin mounts had the guns individually sleeved and had pusher shell hoists for each gun.  Charges were passed by hand.

6) Crew was 10 for the single mounts and 16 for the twin mounts.

7) 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.
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Data from
"Naval Weapons of World War Two" by John Campbell
"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
and
Tony DiGiulian's personal files
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"The Japanese Ships of the Pacific War" by The Koku-Fan
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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