8-inch Coastal Defense Guns
by Dirk H.R. Spennemann
The Types

Two main types of 8-inch guns have been identified, those with short barrels (200mm Short Naval Gun) and those with long barrels. These types break into the following subtypes:

Short Barrel-Type
  • 12 cal. Model 3 (Short) Naval Gun (1943)

Long Barrel Type

  • 25.6cal. MK III (1881)
  • 40cal. (1897)
  • 45cal. (1903)
  • 45cal. Meiji Type 38 (1905)
  • 45cal. 3rd year (1924)
  • 50cal. Mk II (1905)
The data on these guns, as available at the time of writing, are mixed quality. They are summarised in tables 1 and 2 as well as in the following descriptions.

Description of Short Barrel Type

This gun was designed as an (experimental) support weapon to be placed on light-decked armed merchant vessels over 5,000t for use against submarine (surface) attacks and aircraft. A similar weapon was manufactured with a calibre of 120mm, which was used on smaller merchant vessels. In the late stages of the Pacific War the 200mm short naval gun was widely used as a coastal defense weapon, with numerous examples known from Guam, and other bases in the Mariana Islands, as well as from Japanese Islands proper (CinCPac–CinCPOA 1945a, p. 60; OPNAV 1945a, p. 58).

Figure 1. Wartime photograph of a 200mm Short Naval Gun (from CinCPac–CinCPOA 1945)

The guns are described as of light weight, having an interrupted thread breech block and a hydro-spring recoil mechanism with the recoil cylinder mounted on the top of the gun. The gun was mounted on a navy-type pedestal mount. Elevating and traversing occurred by handwheels, both located on the left side of the mount. The rate of traverse was approximately 8.6°/sec, while the rate of elevation was 8°/sec, making it a slow weapon for anti-aircraft fire.

The purpose of this weapon was to deliver a relatively heavy projectile at a limited range for anti-submarine attack and landing operations, and to throw up low-level anti-aircraft barrage.

From available data it appears that one person can operate the weapon, even though the standard complement appears to have been nine, including gun layers and ammunition handlers. With a full complement a rate of four rounds per minute could be sustained.

The ammunition required for the gun was semi-fixed and consisted of a 103 (134) pound shell and a Cu-alloy cartridge (7.2lb) containing the propellant (OPNAV 1945a, p. 61; CinCPac–CinCPOA 1945b, p. 103; U.S. War Office 1953b, p. 505).

Figure 2. Top view of a 200mm short naval gun in operation (after OPNAV 1945, p. 58)

Potential sources of confusion

The 200mm Short Naval Gun can be confused with its smaller design-cousin, the 120mm Short Naval Gun, which has the same overall appearance and design. However, the 120mm gun can be distinguished by (i) a lesser calibre (4.7'), (ii) a shorter barrel (144cm [57 inch] as opposed to 240cm [96 inch]), (iii) a shorter recoil mechanism which does not protrude significantly beyond the gun mount, and (iv) the lack of a large protrusion at the pedestal base.

Figure 3.
Breech view of a 8-inch gun at Sapuk, (#1), Moen Is., Chuuk Atoll.
Note the interrupted screw breech mechanism (photo: D.H.R. Spennemann).


Description of Long-Barreled Types

As has been shown in the type overview, a total of 6 types of long-barreled guns are on record. For convenience, these have been grouped in calibers. One 25.6 caliber gun is on record, two 40 , four 45 and three 50 caliber models are known. The technical data for these guns, where available, have been set out in tables 1 and 2. Those guns encountered so far in Micronesia belong to the 45 and 50 caliber types, on which we will concentrate our discussion.

All guns were wire-wound guns and have been manufactured by the British armament firms W.G. Armstrong-Whitworth and Vickers, Sons & Maxims, or their international subsidiaries. The initial 8-inch guns were manufactured with relatively short barrels, namely 25.6 calibers. Following the overall tend of increasing barrel length and hence penetration power, the barrels were increased to 40, 45 and finally 50 calibers.

40 cal. 8-inch guns

There are a few 40 caliber models known. Armstrong-Pozzuoli manufactured both 38.6 caliber and exactly 40 caliber gun barrels from 1897 onwards. W.G.Armstrong -Whitworth substituted these in about 1905 with larger calibers. It is further possible, that 8-inch guns were also manufactured in license by Vickers-Terni Società Italiana d’Artiglieria ed Armamente, Italy, even though they are not likely to have been used by Japan. The Armstrong barrels used a simple E.O.C. groove rifling. The number of lands could not be determined.

Figure 4. Sapuk, Moen Is. Chuuk Atoll. Rear view of Sapuk #1 8-inch coastal defence gun manufactured by Stabilimento Armstrong-Pozzuoli (1902) (Photo: D.H.R.Spennemann).

Figure 5. Sapuk, Moen Is. Chuuk Atoll. Rear view of Sapuk #2 8-inch coastal defence gun manufactured by Sir W.G.Armstrong–Whitworth (1900?). (Photo: D.H.R.Spennemann).

45 cal. 8-inch guns

45 cal. guns were manufactured by W.G. Armstrong-Whitworth, its subsidiary Stabilimento Armstrong–Pozzuoli, Vickers, Sons & Maxims, and by Nihon Seiko Shi (Japanese Steelworks), the Japanese subsidiary of W.G. Armstrong-Whitworth and Vickers, Sons & Maxims. The 45cal. gun came into service in 1903 in the UK and in 1905 in Japan (thus addressed in Japan as the Type 38 8-inch gun). Guns of this caliber are the most common in Micronesian coastal defense positions. A Vickers, Sons and Maxims 1905 model has a barrel length of 30 feet with 19.2 feet protruding from the shield. Armstrong were of the same sizes. The barrels have two reductions in diameter, one just ahead of the center of gravity (and the trunnion jacket) and one further towards the muzzle.


The rifling of the 45 cal. gun barrel (encountered at Betio) is straight for one fifth of the barrel length and then turns clockwise. One Armstrong-Pozzuoli Gun inspected at Sapuk, Chuuk, had 56 lands.


The base plate carring the hinge of the breech had been screw bolted onto the breech end in both the Armstrong-Pozzuoli and the W.G.Armstrong-Whitworth guns emplaced at Sapuk, Moen Chuuk. In all cases these had been removed. The 8-inch Amstrong-Pozzuoli guns had a pattern, where five slotted and five srew sector were used. There were five grooves of thread on the breech end; then the slotted and screwed sectors were offset and another 8 windings (grooves) followed. The conical, presumably continuous motion breech block was hinged on the right (CinCPac–CinCPOA 1945a, p. 57).

Recoil and Gear

Recoil was buffered by three recoil cylinders mounted underneath the barrel. The elevating gear was located on the right hand side of the gun. Elevation, and traversing were done electrically. The traverse was usually operated by a motor set in a pit underneath the gun turret. Both elevation and traverse could be effected by hand wheels in case of power failure.

50 cal. 8-inch guns

British manufacturers introduced the 50 cal. gun in the early 1920s, but it gained little interest in the UK. Based on the British design, the Japanese subsidiaries at Nihon Seiko Sho and the Kure Naval Yard developed the gun further and produced a Mk II. 50 cal. 8-inch gun in 1924 (known as 3rd year type). These 50 cal. guns were adopted as the main weapon of the Japanese cruisers following the Washington Naval Limitation Treaty.

Table 1. Specifications of 200mm guns encountered or suspected to be present on the Japanese bases in Micronesia
 200mm CD200mm CD200mm CD200mm CD200mm CD200mm CD200mm CD200mm CD
ModelMk III       
Year188118971897 <19051903<1905 
ManufacturerArmstrong- MitchellArmstrong- PozzuoliArmstrong- PozzuoliArmstrong- MitchellArmstrong- WhitworthArmstrong- PozzuoliVickers, Sons & MaximsArmstrong- Whitworth
No. of guns built        
Calibre (mm)203203203203203203203203
Calibre (inch)8888.18888
Length overall (inch)225.6373.5    372.1 
Length overall (calibres)28.246.7    46.5 
Length of bore (inch)204.8308.9 320.0360.0360.0360.0400.0
Length of bore (calibres)25.638.61404045454550
Weight of barrel (lbs) [1]29,12043,87239,68331,00040,32042,67342,16847,040
Muzzle velocity (ft/sec)1,9532,5592,4602,2422,6002,5262,8503,000
Muzzle energy (tons/foot)5,54016t/sqinch 7,41311,78110,96014,08015,600
Max range horizontal (yds)  17,80022,000    
Max range vertical (feet)        
Effective range vertical (ft)        
Rate of fire (rounds/min)  465465
Practical rate of fire  354344
Elevation   30    
Weight of projectile (lbs)210269/256250/250250250/230250250
Type of projectile HE/APAP/HEAP shot, AP shell AP/HE  
Type of ammunition   SATSAT SATSAT
Principal Charge10051.8  66 9490
Length of recoil (inch)        
Penetration at muzzle (inch)    29.6 31.135.7
No. of lands    3256  
Twist    00- 30   
Rifling system        
The data presented in this table have been culled from the following sources, leading to some unavoidable inconsistency: Brassey 1905; CinCPac- CinCPOA 1945d, p. 58; Fraccaroli 1970, p. 281- 2; Jane 1904, p.203; Jane 1990; Jentschura et al. 1977, p. 10; Parkes 1966, p. 316. Note also that at the time of writing not all data were available to the author.
Table 2. Specifications of 200mm guns encountered or suspected to be present on the Japanese bases in Micronesia.
For sources see table 1
 200mm CD200mm CD200mm CD'Short' 200mm'Short' 200mm
Model3rd Year (Mk.II)Type 38 3rd Year (?)3rd Year
Year19241905<1905 1943
ManufacturerKure NYNihon Seiko ShoVickers, Sons & Maxims Kure NY
No. of guns built     
Calibre (mm)203 203203203
Calibre (inch)8 888
Length overall (inch)  412.13  
Length overall (calibres)  51.51  
Length of bore (inch)400360400 80
Length of bore (calibres)504550 12
Weight of barrel (lbs) [1]  37,968  
Muzzle velocity (ft/sec)  3,3003101,016
Muzzle energy (tons/foot)  16,360  
Max range horizontal (yds)   6,5006,900
Max range vertical (feet)   10,50010,750
Effective range vertical (ft)   9,000 
Rate of fire (rounds/min)  645
Practical rate of fire  43 
Elevation   6575
Depression   1515
Weight of projectile (lbs)276/383 216.7/AP134103/HE
Type of projectileAP/HE APAPSH, AP, HE, AA, IN
Type of ammunitionSFSFSATSFSF
Principal Charge  123.57.1 
Length of recoil (inch)     
Penetration at muzzle (inch)  34.6  
No. of lands     

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Bibliographic citation for this document

Spennemann, Dirk H.R. (2000). 8-inch Coastal Defense Guns. British, Italian and Japanese Naval Guns and their Emplacements in Micronesia.
URL: http:/marshall.csu.edu.au/Marshalls/html/Sapuk/Sapuk.html

Dirk H.R. Spennemann, Institute of Land, Water and Society, Charles Sturt University, P.O.Box 789, Albury NSW 2640, Australia.
e-mail: dspennemann@csu.edu.au

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