British Naval Heritage in Micronesia:
Tangible evidence of the armament trade from 1890 to 1937
by Dirk H.R. Spennemann

Chapter 4. 150mm Coastal Defense Batteries

The typical coast defense battery consists of three gun emplacements set in line, usually at or close to the water's edge. The revetments in a coast defense battery are commonly set about 22 to 25 m apart (CINPAC-CINCPOA 1945a:54). The quarters for gun personnel were located to the rear and outward flank from each emplacement (MID 1945:105). To the rear of the battery is a concrete built ammunition storage building.

Occasionally, however, a single coast defense gun emplacement can be found, such as at the southern tip of Mile Island. The emplacements were standardised and the lay-out of the battery was the same all over. The schematic lay-out of such a battery is shown in figure 5.

A completely developed coastal defense gun battery comprises of the following entities (reference is made features on figure 5): A group of three six inch coastal defense guns in their emplacements (8) are set in a row along the water's edge, flanked by two medium anti-aircraft guns (75 or 80mm) in their emplacement (7). The anti-aircraft defense is further strengthened by three heavy machine gun emplacements (9). A heavy machine gun or medium anti-aircraft battery consisting of four emplacements is set to the rear of the ammunitions building and the command centre (13). The fire control center (6) and an auxiliary building, possibly serving as a generator building (5) are set to the rear of the central coastal defense gun emplacement. The ammunition building (4), set in a strong earth revetment is set further to the rear, and is connected to the gun emplacements by access roads (10) and by narrow gauge railroad tracks (16). The latter is being used to haul the 100lb heavy shells to the gun emplacements.

The barracks building for the gun crews (1) is set to one side, together with a bath (2) and a toilet building (3). The coastal defense gun battery is defended against attacks from the seaward side by barbed wire entanglement and obstacles for beach defense (11) set onto the beachrock outcrops and the coral reef platform. A personnel trench to guard against landings has also been dug (13). Against attacks from the landward side, an angular, slotted personnel trench (12) has been dug, which is strengthened by a series of heavy machine gun emplacements (14).

The ground defenses vary from gun battery to gun battery. In many cases there are additional, personnel trenches of short length and additional light and medium machine gun emplacements.

Figure 5. Schematic lay-out of a 150mm coastal defense battery. 1--Barracks building for gun crews; 2--Bath building for gun crews; 3--Toilet building for gun crews; 4--Ammunition magazine in earth revetment; 5--Auxillary Building (generator building?); 6--Fire control center; 7--Anti-aircraft gun (medium) in emplacement; 8--Six inch coastal defense gun in emplacement; 9--Heavy machine gun (anti-aircraft); 10--Access road system; 11--Barbed wire entanglement and obstancles for beach defense; 12-- Slotted personnel trench to guard against attacks from the landward side; 13--Personnel trench to guard against attacks from the seaward side; 14-- Heavy machine gun emplacements to ward off attacks from the landward side; 15--Heavy machine gun battery (anti-aircraft); 16--Narrow gauge railroad to deliver shells to the coastal defense guns.

Composition of batteries

The guns emplaced in these batteries are commonly of the same type. That is, either three British manufactured guns were used in a battery, or three Japanese ones. In addition, as far as the Marshall Islands bases are concerned, it appears that even within the British manufactured guns emphasis was placed on the type of guns, thus putting only three guns of the 1898 batch together, or three guns of the 1905 batch. A variation of this pattern is reported from Kiska, Aleutian islands, where the Japanese had very rapidly erected an advanced base. On Kiska one gun battery consists of two guns made by the Kure Naval Arsenal and one made by Armstrong Whitworth & Co Ltd. (Model 1900). The other battery consisted of two guns manufactured by the Kure Naval Arsenal and one gun manufactured by Sr Armstrong Mitchell (Model 1894).


The emplacement of the 150mm guns commonly consisted of a circular, slightly deepened revetment (figure 6) of 10.5-11.5 m in diameter (CinCPac-CinCPOA 1945a:54) The revetments sloped on their outer sides and are build of coral boulders and concrete. Similar types of emplacements have been found on Betio, Tarawa Atoll, Kiribati, where the ready ammunition magazines were located only on the landward side of the gun emplacement (JICPOA 1945c:69-70). However, exceptions are also known. An open boulder revetment shielded the 150 mm CD guns at Kiska, Alaska (JICPOA 1945c:73). An open coral boulder revetment shielded the 140 mm CD guns at Saipan (JICPOA 1945c:74). In the Marshall Islands both concrete and concrete/coral boulder revetments occur.

The assessment of bombing effects showed that in many cases a revetment could sustain several direct bomb hits without breaking its inner wall or putting the gun out of the operational category. A study on the efficiency of the bombing by dive-bombing SBD-5's found that the gun emplacements would stand out well as long as they had not been the focus of bombing raids. Once they had been bombed severely, the round bomb-craters with their surrounding wall of soil could easily be mistaken for the gun-emplacements (U.S. Marine Corps 1944i).

Figure 6 Standard 150mm gun emplacement.

Fire Control

Commonly a six-inch gun battery had a couple of three-meter range finders and a fire control center located in a covered building (Verbeck 1943:17). Fire control of the battery would be effected by a fire control center, set in a building at the rear of the central emplacement. Here all information from the fire observation posts and from the guns would converge. On most bases the fire control was a concrete structure. The fire control towers on Mile, for example, had been erected on wooden towers or on a concrete building, as in case of the southwestern 127mm DP battery.

The range finder is also known to have been erected on loosely concreted coral boulder mounds, as on Kwajalein (JICPOA 1945c:36) or on wooden constructions, made of coconut logs, as on Makin, Kiribati (JICPOA 1945c:37) During the time of the operations several range finders were apparently set on small observation towers erected from coconut logs. These could easily be destroyed even by near-misses and no traces of such structures have survived. See for example the toppled range finder position of the southern 140mm gun battery formerly erected on coconut logs (USSBS 1947a:247 photo 8).

Ammunition Ready Magazines

Each of the emplacements had recesses for ammunition ready magazines. The ready ammunition magazines, horizontally revetted into the wall of the gun emplacement are set at an interval of 60deg., with the exception of the seaward side, thus providing four magazines. These ready magazines consisted on metal boxes with a hinged access door at one end (figure 7). The door could be opened all the way, flush with the side of the box, so that it could be slid into the concrete recesses of the emplacements. Inside the box were a metal sheet, set close to the opening, which would show eight perforations. A wooden plank, set at the internal end of the box, would also have eight holes, destined to receive a complete round each (see above). The plank of wood at the internal end was necessary in order to prevent the fuses from becoming scratched, otherwise accidentally damaged, or even set off. The walls of the boxes are padded with what appears some sort of asbestos material, most likely to prevent an accidental fire from causing havoc with armed shells inside the ready box.

Figure 7. Ammunition ready magazine for a 150mm gun position.

Ammunition Magazines

The ammunition for the guns was stored in concrete ammunition magazines. These buildings would be set in a low earth embankment, to avoid the base of the magazine from being damaged by close-up bombs. The buildings would have a large internal room with a suspended wooden ceiling and a ceiling crane facilitating the movement of the heavy shells inside the buildings. the buildings have an access ramp, protected by a double set of bomb blast doors with inch thick plating

A narrow gauge railroad, the most ubiquitous remains of which are the axles of the railroad carts, serviced the gun emplacements with the heavy shells from the magazine. As far as can be ascertained, the ammunition railroad used only hand driven carts and no locomotives.


The six inch guns were operated by a crew of nine men under the command of a gunnery officer of the IJN, commonly with the rank of a lieutenant. For servicing a battery of three guns 63 men were needed (CINPAC-CINCPOA 1945a:54). The crew would sleep in a barracks building to the rear of the battery in one of various standard-type barracks buildings (see Denfeld 1979; Look & Spennemann 1992 for illustrations).


The crew were housed in a barracks building close to the gun emplacements. These barracks buildings existed in a variety of combinations of internal lay out, depending on function. All buildings had in common an elevated floor set on concrete support posts, wide eaves with a covered verandah, and large open windows to allow for breeze and fresh air.

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Bibliographic citation for this document

Spennemann, Dirk H.R. (2000). British Naval Heritage in Micronesia: Tangible evidence of the armament trade from 1890 to 1937. Albury:
URL: http:/

Dirk H.R. Spennemann, Institute of Land, Water and Society, Charles Sturt University, P.O.Box 789, Albury NSW 2640, Australia.

(c) Dirk H.R. Spennemann 1993-2000
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