TheJapanese20cmdualpurposegunattheNavalMagazine,Guam.– TheappearanceoftheguninJune1994—

DirkHRSpennemann InstituteforLandWaterandSociety;CharlesSturtUniversity†

This brief report was written as a background document in partial response to a request for information on the possible conservation of Japanese guns on public display at the Navy Base, Guam (Bulgrin, 2017). This document has two aims: i) to compile the available technical data on the short-barrelled 20cm naval gun, and ii) to provide photographic data on the appearance of the gun in June 1994, when it was photographed as part of a metal conservation course (Look & Spennemann, 1994).

Japanese anti-aircraft and coastal defence during the latter part of the Pacific War relied increasingly on medium calibre weapons, such as the 20cm (8-inch) and 12cm (4.72-inch) guns, which could be relatively easily emplaced (Spennemann, 1994a, 1994b).

The 20cm 12 cal. Model 3 (Short) Naval Gun (1943) The sections under this heading have been extracted from an in-depth description of the 20cm Model 3 (Short) Naval Gun provided elsewhere (Spennemann, 2017d).

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. While theoretically also functional as a heavy anti-aircraft weapon, U.S. intelligence services did not deem it to be very effective in that role (CinCPac–CinCPOA, 1945b, p. 60). The 20cm guns had a moderate range of 6,900 yards. 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 capable of a 360º traverse. Elevating and traversing occurred by hand wheels, both located on the left side of the mount. The rate of traverse when operated by hand was approximately 8.6°/sec, while the rate of elevation was 8°/sec, making it a slow weapon for anti-aircraft fire (CinCPac–CinCPOA, 1945b, p. 60; OPNAV, 1945, p. 58; USNTMJ, 1946b, p. 16). The gun was not fitted with individual fire control systems (USNTMJ, 1946b, p. 16).

From available data it appears that one person could 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 technical data for the gun have been summarised in Table 1. Post-World War II assessment of guns and gun mounts held by the Kure Naval Arsenal showed that the gun was constructed in three subtypes or variants (USNTMJ, 1946b, p. 10), the details of which appear not to be documented. 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 (CinCPac–CinCPOA, 1945a, p. 103; OPNAV, 1945, p. 61; U.S. War Office, 1953, p. 505; USNTMJ, 1946a, p. 13).

Even through primarily designed as a naval weapon to be carried afloat, the 20cm short naval gun found intensive use as a coastal defence weapon in the late stages of the Pacific War (see below for locations). They were sited in a variety of emplacements: open emplacements, similar to those used for other calibres, open earth covered emplacements, concrete revetments, concrete reinforced casemates and cave positions with concrete or coral boulder embrasures. The local environment governed the choice of emplacement and concealment.

Preferred citation for this document: Spennemann, Dirk HR (2017) The Japanese 20cm dual purpose gun at the Naval Magazine, Guam. The appearance of the gun in June 1994. Albury NSW: Institute for Land Water and Society; Charles Sturt University.

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Figure 1. Wartime photograph of a 20cm Short Naval Gun in an open emplacement (CinCPac–CinCPOA, 1945b).

The short-barrelled 20cm guns are absent on the earlier Japanese bases (Look & Spennemann, 1993a; Spennemann, 2008a, 2008b; Spennemann & Clemens, 2014). They were installed as coastal defense guns during the latter part of the Pacific war, mainly in beach situations where their plunging fire could serve to interrupt landing operations.

The short-barrelled 20cm guns have been reported as coastal defence guns from Western Micronesia, such as Peleliu, Palau (Denfeld, 1988, p. 71); Saipan (Spennemann, 2017c); and especially from Guam, where they are on record for: Bangi Point, Guam (Denfeld, 1992, p. 51); ‘Gongna Beach (‘Gun Beach’), Tumon Bay, Guam (Spennemann, 2017a); Dungcas Beach, Tamuning, Guam (in replica emplacements on the grounds of the Onwards Beach Hotel) (Spennemann, 2017e); Naval Magazine, Guam (on display) (this report); and Ga’an Point, Agat, Guam (on public display)(Spennemann, 2017b).

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Table 1. Technical data of 20cm short naval guns. Various sources

Model 3rd Year Year 1943 Manufacturer Kure Naval Yard Calibre (mm) 203 Calibre (inch) 8 Length overall (inch/cm) 100/252 Length of barrel (inch/cm)1 95.9/243.8 Height overall (inch) Length of bore (inch) 80 Length of bore (calibres) 12 Weight with breech (lbs/kg) 1,390/630 Weight overall (lbs/kg) 1,702/772 Muzzle velocity (ft/sec, m/sec)

1,016 / 305

Max range horizontal (yds/ m) 6,900 / 6,300 Max range vertical (feet / m) 10,800 / 3,300 Effective range vertical (ft) 9,000 Maximum rate of fire 4-5 Practical rate of fire 3 Approximate Lifespan 2000 service rounds Traverse 360° Elevation 75° Depression –15º Rate of Traverse 8.6°/sec (hand) Rate of Elevation 8°/sec (hand)

Breech system interrupted screw Chamber length (in / cm) 16.1 / 39.5 Chamber volume (cu.in / l) 891 / 14.6 Length of recoil (inch) 10 Type of rifling raised Nº of lands 32 Groove depth (mm) 1.5 Rifling system left turn,

increasing 1/30 to 1/13 Recoil system hydro-spring number of guns manufactured ca 250 Loading angle 10º Loading support land-based: simple

derricks ships: cargo hoists

Ramming by hand Type of ammunition semi-fixed round Type of projectile anti-aircraft, armour

piercing, high explosive, incendiary,

incendiary shrapnel Weight of projectile (lb/kgs) HE 103 / 47 Type of charge casing brass, later steel Weight of charge (lbs / kg) 4.4 / 2 Type of mount pedestal Total weight (tons) 3.5 (4.1)

Figure 2. Location of the Naval Magazine in relation to Ga’an Point and Bangi Island (open circles).

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Photographic documentation of the gun at the Naval Magazine, Guam The 20cm gun is kept on public display in front of the Commandant’s Office of the Naval Magazine, Guam (Figure 4) (Coordinates 13.385435, 144.684851). According to the manufacturer’s stamp, the gun carries the serial number 59 and was manufactured in 1943 at the Kure Navel Yard (Figure 25).

The origin of the gun has not been ascertained at the time of writing. It is likely to have come from one of the emplacements at Agat Point or Bangi Island (Figure 2). A private image, taken in 1944, shows a single gun sitting on an unidentified beach on Guam. It is not emplaced and looks ready for rabsportation to another location. In the absence of identifying characterises, it can only be speculated that this is the gun under discussion.

Figure 3. Short 20cm naval gun on an unidentified beach at Guam, The gun is ready for transportation to another location.2

The gun was inspected in late June 1994 as comparison to a 20cm gun displayed at Ga’an Point, Agat (Spennemann, 2017b), which at that time was being treated as part of the metals conservation course and demonstration project ‘Conservation Management of Historic Metal in Tropical Environments’ (Look & Spennemann, 1994).

While corrosion is generally accelerated in tropical environments, this is particularly the case for coastal defence guns. By their purse, such guns are emplaced at the shoreline and therefore continually exposed to salt-laden, moist air (Look & Spennemann, 1996). While larger guns tended to be emplaced on elevated positions in order to increase their range (e.g. Spennemann, 2006; Spennemann, 2008c), the short 20cm naval guns were emplaced at or near beach level, often in secluded positions that provided for a wide field of fire over potential landing beaches. The situation is often exacerbated by encroaching vegetation, which maintains a humid microclimate (Spennemann & Look, 2006). The environmental conditions are such that conservation management in situ is likely to result in substandard treatment, requiring the gun to be temporarily relocated to a semi-climate controlled facility (Look & Spennemann, 1993b, 1994).

At the time of inspection in June 1994, the 20cm naval gun at the Naval magazine was by far the best preserved specimen the convenors of the Metals Conservation Course (Look, Spennemann) had inspected. It was intimated that the gun had been kept in dry storage since the end of World War II and only been placed on open-air display one or two years prior. The verbal recommendation was made that because the gun had such a high integrity and thus had high significance as a heritage item, it should be returned to dry storage as soon as feasible and the limited corrosion be treated.

The following images of the gun were taken in June 1994, but no formal documentation had been carried out.

Dirk HR Spennemann, The Japanese 20cm dual purpose gun at the Naval Magazine, Guam

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Photographic documentation of the gun at the Naval Magazine, Guam

Dirk HR Spennemann, The Japanese 20cm dual purpose gun at the Naval Magazine, Guam

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Figure 4. Setting of the 20cm naval gun, as emplaced at the Naval Magazine, Guam.

Note the Japanese 47mm Type I field gun at right.

Figure 5. View of the gun, left side, as emplaced at the Naval Magazine, Guam.

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Figure 6. View of the gun, seen from front right, as emplaced at the Naval Magazine, Guam.

Figure 7. View from the left rear.

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Figure 8. View from the right rear.

Figure 9. View of the left side.

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Figure 10. View from the front

Figure 11. View from the rear

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Figure 12. Note the gun mount, seen from the front left. Note the elevation indication which

has been painted over.

Figure 13. View of the left side, showing the traversing wheel.

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Figure 14. View from the front left, showing the traversing wheel

Figure 15. View of the breech and pedestal, seen from the rear right. Note the standing water

in the pedestal base.

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Figure 16. View of the right side of the pedestal. Note the emerging vegetation.

Figure 17. View of the pedestal base seen from the front.

Figure 18. Oil reservoir for the recoil system, seem from the front left

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Figure 19. View of the top of the Monobloc breech section.

Figure 20. The recoil cylinder, seen from the front left. Note the shackle used for the movement

and emplacement of the gun.

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Figure 21. The shell loading tray is still moveable..

Figure 22. Crevice corrosion at the recoil system.

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Figure 23. The lands of the gun barrel.

Figure 24. Inscription on the left side of the gun block.

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Figure 25. Inscription on the left side of the gun block (enhanced detail). ��� ��%�� ��� �

<3> ��� � $����

Kure Nº 59 Kure Naval Yard Short 20cm Gun

(3) Showa 18th year

Manufacture Nº 5375

Figure 26. Inscription on the right side of the gun block.

()���� (Weight 772 kg).

Dirk HR Spennemann, The Japanese 20cm dual purpose gun at the Naval Magazine, Guam

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Figure 27. Inscription on the oil reservoir for the recoil system

Figure 28. Inscription on the oil reservoir for the recoil system (see Figure 27). Image rotated

clockwise 90º Transcription and translation below.

��� #&��+,"��* �'!��������

Caution Be sure to properly lubricate the internal parts when assembling the gears

Dirk HR Spennemann, The Japanese 20cm dual purpose gun at the Naval Magazine, Guam

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Figure 29. Visitor impact. Accumulation of rubbish inside the gun barrel.

Figure 30. Visitor impact.

Acknowledgments I am very much indebted to the following for kindly assisting in the transcription of the Kanji characters on the gun: Ken Bryson (Decatur, GA), Koji Kanemoto (Long Beach, CA), and Minoru Shiroyama (Takasago, Hyogo Prefecture, Japan). Several historic images were kindly furnished by Nina Peck (Museum Technician, WAPA, US NPS Guam).

Endnotes

† Contact of the author: Dirk HR Spennemann, Institute for Land Water and Society; Charles Sturt University; PO Box 789; Albury NSW 2640, Australia. E-mail: dspennemann@csu.edu.au.

1 Breech face to muzzle. 2. Image courtesy of Flickr user ‘MintChocolate2.’ Image URL: https://www.flickr.com/photos/100937980

@N02/ 21223131814 <accessed 20 May 2017>.

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