The following information about the Japanese defense of Betio Island
is based on a joint study made by Marine Corps, Army, and Navy intelligence
personnel.1 The fundamental points brought out by this study are
presented in the Intelligence Bulletin so that they may be widely
disseminated, particularly among junior officers and enlisted men of the Army.
That the Japanese organized their Betio defenses for an all-around, decisive
struggle to keep United States forces from reaching the beaches is borne out
by a study of the map on pages 34 and 35. This map, drawn to scale, is
designed to show an over-all picture of the enemy defensive
setup. The insets show important areas in detail.
The Japanese beach defenses consisted of well-emplaced and well-sited
weapons, various types of obstacles, and mines. The weapons included
grenades, mortars, rifles, light and heavy machine
guns, 13-mm dual-purpose machine guns, 37-mm guns,
70-mm infantry guns, 75-mm mountain
guns (Model 41), 75-mm dual-purpose
guns (Model 88), 80-mm antiboat guns, 127-mm
twin-mount, dual-purpose guns, 140-mm coast-defense
guns, and 8-inch coast-defense guns.
The obstacles included pyramid-shaped, reinforced concrete
obstacles, which were placed about halfway around the island
on the coral reef; an antiboat barricade, made of coconut-palm
logs: double-apron barbed wire; a perimeter barricade, constructed
chiefly of coconut-palm logs; and antitank ditches, dug a short
distance back of the perimeter barricade.
Antipersonnel and antiboat mines were laid on the fringing reef—frequently
between the concrete obstacles—and on the beaches.
Several Japanese flame throwers, were found.
Appropriate fire-control equipment was installed for the coast-defense
and antiaircraft batteries, including range finders, directors, and
searchlights. The weapons, as a rule, were mounted in strongly
constructed emplacements made of coconut-palm logs, reinforced
concrete, and revetted sand.
The Japanese employed the 13-mm (approximately .50 caliber)
machine gun as their basic beach-defense weapon along the entire
north coast and on both sides of the eastern tip. Along the western and
southwestern coasts, the 7.7-mm heavy machine gun was the
The organization for defense inshore was haphazard. Beaten on the
beaches, the Japanese fell back to bomb-proof ammunition shelters
and personnel shelters inshore from the beaches, and fired from
the doors of the shelters. These were blind to attack from
several directions; they were not designed as blockhouses, and
had only a few firing ports.
a. Reinforced Concrete Pyramids (tetrahedrons)
Almost up to the time United States Marine forces landed on
Betio, the Japanese were working rapidly to surround the island
with pyramid-shaped, reinforced concrete obstacles on the
fringing reef. The process was approximately half completed
at the time of landing. Figure 1 shows how the enemy had been
molding these obstacles on the beaches. Before concrete
was poured into the inverted forms, the angle irons which
formed the corners and horns were driven into the ground.
|Figure 1.—How Japanese Molded Concrete Obstacles.|
The actual size of the obstacles varied. Their bases usually were
about 4 feet wide and their height was determined in
accordance with the average height of the water over the
reef. The center-to-center distance between the obstacles
varied from 6 to 20 feet, on different beaches.
Located about midway out on the reef, these obstructions were
just high enough to break the water at high tide. They were
designed to obstruct landing boats or to canalize them into
predetermined areas which could be swept by the fire of
antiboat guns, ranging from 13-mm machine guns
to twin-tubed 127-mm guns.
In addition to the reinforced concrete obstacles, the
Japanese rounded out their reef defenses by using wire,
barricades, mines, and fairly large piles of coral
rocks, which in some areas were staggered among the
pyramids and strewn about the reef. The rocks were
from 6 to 18 inches in diameter, and the piles
were 4 to 6 feet high.
The Japanese used three types of wire obstacles: high double-apron
fences, low double-apron fences, and single-apron fences.
The high double-apron wire was placed inshore of the pyramidal
obstacles and below the high tide mark. It was constructed to
canalize assaulting troops into direct enfilade fire from
emplaced light and heavy machine guns and into trip wire.
Immediately inshore from the beach, high double-apron wire was
placed directly in front of tank ditches, and low double-apron
wire was placed behind the ditches.
Low double-apron wire was placed above the high-tide mark, and
was employed to canalize or obstruct assaulting troops in front
of covered machine-gun emplacements.
Single-apron wire was erected in front of some portions of the
log barricades. The wire was strung from the tops of vertical
logs to stakes in the sand forward of the barricade.
c. Antiboat Barricade
On the south beach of Betio, the Japanese constructed an antiboat
barricade with coconut-palm logs (see fig. 2). The barricade,
which was 10 feet high, was shaped like a wide V, with
one leg 700 yards long and the other 300 yards long. The
logs were secured in place with wire and soft steel fasteners, 1/2 inch
|Figure 2.—Japanese Antiboat Barricade.|
The barricade was planned to divert landing boats to the east and
west of the center of the beach, and into areas which would receive
flanking fire from emplaced heavy machine guns, dual-purpose
guns, and heavy antiboat guns.
d. Perimeter Barricade
The Japanese constructed a barricade of coconut logs around virtually
the entire perimeter of the island (see fig. 3). There were a few
unbarricaded spaces, but these were protected by antitank ditches. Many
of the perimeter-defense emplacements, because of the nature of
their construction, were in themselves good barricades. (These
are described later.)
Each coconut-log barricade followed one of three general
designs: (1) Log barricade with built-in rifle or light
machine-gun emplacements (see fig. 4); (2) log barricade
without built-in weapon emplacements (see fig. 3); and (3) tree
stumps laid with their bottoms facing the sea.
|Figure 3.—Japanese Beach Barricade.|
|Figure 4.—Japanese Beach Barricade (with
built-in rifle or light machine-gun emplacements).|
That portion of a barricade which did not have built-in and covered
rifle or light machine-gun emplacements had, instead, open sandbagged
emplacements behind the barricade for these weapons.
e. Antitank Ditches
Antitank ditches on Betio were only 5 to 7 feet deep—because the
water table was about 8 to 10 feet below the surface—and
were 12 to 14 feet wide. Only one ditch was revetted—with coconut-palm
logs on the opposite side of the expected tank approach.
Wire obstacles were placed on a road at points where antitank ditches
formed a junction. Covered machine-gun emplacements were sited at the
ends of some antitank ditches. Apparently antitank-gun fire was to
be supplied by 37-mm, 70-mm, and 75-mm
On the south beach, one antitank ditch was located about 10 yards
inshore from a line of coconut-palm stumps. Machine guns emplaced under
cover and 37-mm guns emplaced without overhead protection
were located inland to provide direct covering fire for the antitank
ditch. At other points along the south beach, short sections of antitank
ditches took the place of barricades.
Four types of mines were used by the Japanese on Betio: Model 93
antivehicle mine, Model 99 armor-piercing mine (magnetized), an
antitank mine, and an antiboat mine.
The Model 93 was used primarily against personnel. This mine is
usually placed in patterns of diagonal rows, with the mines
about 30 inches apart. The brass plug on top of each mine is
generally at ground level. The device is activated by pressure on the plug.
The Model 99 (magnetic) mine was used primarily against tanks
and armored cars.
The antiboat mine was found in large numbers on the south and west
coasts. It is believed that the Japanese were in the process of encircling
the island with these mines at the time the United States
Marines landed. Along the south beach the mines were located
between the double-apron wire and the shore. Laid in a double lane
paralleling the beach line, they were placed about 20 yards
apart. In some places the mines were covered by 2 to 3 feet of
water at high tide, while in others they were dry both at high and
Only a few of the antitank mines were found. These were buried in
the sand, with their necks exposed.
4. GRENADE DISCHARGERS AND GRENADES
The Japanese used Model 89 grenade dischargers and two types of
hand grenades against landing boats and personnel. The grenade
dischargers apparently were assigned by sections throughout
the beach-defense system. In addition, several sections were
placed behind antitank ditches in the eastern portion of the
5. RIFLE AND LIGHT MACHINE-GUN EMPLACEMENTS
Light machine-gun emplacements and rifle emplacements (or pits) were
constructed to accommodate these weapons interchangeably. Most of
the emplacements were located directly in the beach barricade. Some
of these were protected by a strong cover, while others were
open. Located close to the beach barricade were several light
machine-gun emplacements made of concrete.
b. Covered Type
The covered emplacements in the beach barricade were topped with at
least one layer of coconut-palm logs about 10 inches in diameter
and with loose sand and coral at least 1 foot
thick (see fig. 4). Inside, these emplacements were 4 feet
long, 4 feet wide, and 4 feet high. The occupant or
occupants were protected by a thick blast wall, located so close
behind the emplacements that entrance was difficult (see fig. 5).
|Figure 5.—Rear View of Japanese Rifle or Light Machine-gun
Emplacements (showing type of construction, blast walls protecting
entrances, and the spacing between each pit).|
Each of these emplacements had a small firing port, 12 inches
long and 6 inches wide, which permitted little more than
frontal fire. Inside, under the firing port, there was a small
fire step or shelf on which a light machine gun could have been placed.
Some of the covered rifle emplacements connected at the rear with
communication trenches, which were revetted with vertical logs,
boards, wire drums, and corrugated sheet steel. Some of these
trenches were covered.
c. Open Type
The open emplacements in the barricade system were mere slots
behind the log wall, protected on the sides by logs bracing the
barricade, by sand, and by a board revetment (see fig. 6). Only
rifles and light machine guns could be fired from these emplacements.
|Figure 6.—Japanese Open-type Rifle or Light Machine-gun Emplacement.|
Some of the open-type emplacements were located a few feet behind, and
above the top of, the barricade. These emplacements were
constructed of sand and were revetted with corrugated sheet
steel and logs.
d. Concrete-pillbox Type
Figure 7 shows a light machine-gun emplacement made of reinforced
concrete and provided with three firing ports. Most of these
emplacements were built just forward of the beach barricade, and
were sited so as to provide frontal fire to cover tactical
wire, and flanking fire to cover the front of the barricade. Since
other emplacements in the vicinity of the concrete pillboxes
provided flanking and frontal fire, the pillboxes may have been
designed primarily for firing on targets of opportunity.
|Figure 7.—Japanese Reinforced-concrete Emplacement (provides
both frontal and flanking fire for light machine guns).|
The tops and sides of the concrete emplacements had an average
thickness of 14 inches; they were reinforced by steel
rods 1/2 inch in diameter.
Although these emplacements were independent of the beach barricade
emplacements, they were connected with the barricade by tunnels,
communication trenches, and blast bays made of logs and concrete.
e. Shields for Riflemen
Figure 8 shows details of two types of shields for riflemen. The
shields, found near the main runway of the Betio airfield, are
light and easy to carry; therefore, in effect, they are mobile
rifle emplacements which afford some protection. They are only 1/8 inch
thick, but are made of hardened steel. They were painted a dull brown.
|Figure 8.—Japanese Rifle Shields (top view—for
use on runways or other hard-surface areas; bottom view—for use on
6. HEAVY MACHINE-GUN EMPLACEMENTS
a. Built into Beach Barricade
Most of these were encountered in the strongly organized and
well-constructed barricade system on the west and southwest
coasts. Within this system, the heavy machine-gun emplacements were
spaced at fairly regular intervals, and were separated by covered rifle
and light machine-gun emplacements, which afforded local protection.
Roughly, the built-in emplacements were of two types: those with a
single firing port, for frontal fire, and those with two firing
ports, for flanking fire. Both types were made of logs and sand, and
were an integral part of the beach barricade.
The single-port type provided frontal fire over the reef and covered
the approaches to machine-gun emplacements which were sited for
Most of the single-port types were well designed and constructed (see
fig. 9). The sides and top consisted of two or three layers of
coconut logs and a layer or two of sandbags covered with sand and
coral. The sides were banked with sand to add protection and
|Figure 9.—Japanese Heavy Machine-gun Emplacement (as an
integral part of a beach barricade).|
The outside width and length of these emplacements were 18
to 20 feet. Inside, they were divided into compartments, one
or more of which were used to store and protect ammunition—these
were always in the rear.
Most of these emplacements were connected with bomb shelters, rifle
and light machine-gun emplacements, command posts, and ammunition
dumps by means of revetted communication trenches.
The two-port type of heavy machine-gun emplacement could mount two
heavy machine guns (7.7-mm) and could possibly
mount 13-mm machine guns. The firing ports in nearly
all cases were sited for flanking fire along the tactical wire
entanglements and boat obstacles. In fact, the design of the
emplacements prohibited frontal fire.
The top and sides consisted of two, and sometimes three, coconut
logs, which were covered by two layers of sandbags and rounded off
at the sides with sand and coral. The finished structure, except
for the entrance and connecting communication trenches, appeared
from the top as a large sand mound within the barricade.
The outside length and width of these emplacements measured
approximately 24 feet. Inside, they were divided into
compartments to give added protection to both personnel and
ammunition. The latter was kept in a separate, well-constructed
room in the rear of the emplacements (see fig. 10).
|Figure 10.—Rear View of Japanese Heavy Machine-gun
Emplacement (showing ammunition storage room in rear; entrance; and rifle or
light machine-gun emplacement to left).|
A second type of twin-port heavy machine-gun emplacement (or
casemate) was made of concrete. Only two of these were found. Each
had two ports, for flanking fire, and each had two adjoining
antiaircraft emplacements. Although this type of emplacement
apparently was designed for the use of 13-mm machine
guns, indications are that 7.7-mm machine guns were
used in the two found on Betio.
b. Outside of Beach Barricade
Open-type heavy machine-gun emplacements in the interior of the
island consisted of simple circular pits dug
into the ground and revetted with boards, corrugated sheet
steel, and sandbags (see fig. 11). Logs and oil-drum pedestals
were used as mounts for guns. These emplacements obviously were
designed primarily for antiaircraft fire (probably 7.7-mm machine
guns). They were located at irregular intervals around the
airfield and inshore of the barricades.
|Figure 11.—Japanese Open-type Heavy Machine-gun
Emplacement (primarily for antiaircraft).|
Apparently the Japanese did not construct any single-port, covered
heavy machine-gun positions inshore of the beach barricades. However, as
the situation developed, the enemy made full use of the entrances
to bomb-proof shelters as machine-gun firing positions.
7. 13-MM MACHINE-GUN EMPLACEMENTS
In defense of Betio, the Japanese employed both single- and
twin-mount 13-mm dual-purpose machine guns. All were
pedestal-mounted, and were located in open emplacements to permit
antiaircraft fire, as well as fire on ground troops. Most of these
guns were sited so that frontal or flanking fire could be placed
on the beach and reef. Several were located on top of high
structures, such as the magazines near the 127-mm dual-purpose
b. Single Mount
Emplacements for the single-mount gun were approximately 4 feet
deep. The gun pedestals generally projected almost to the ground
level; thus the gun itself was only 1 to 1 1/2 feet
higher (see fig. 12).
|Figure 12.—Emplacement for Japanese
Single-mount 13-mm Machine Gun.|
In construction, these emplacements varied as follows:
(1) Six-sided emplacements, 10 feet in diameter, with the retaining
walls consisting of a layer of horizontally placed logs, or boards
and logs, or sandbags, and a sandbag parapet. In many of these
emplacements, the parapets were two or three sandbags higher
than others—presumably for protection against blast and
fire. In at least one position, communication trenches led to
(2) Ten-foot-square emplacements, with log and sand-constructed
shelters 6 1/2 feet high and 10 to 15 feet wide. These
emplacements had coconut-log retaining walls which were banked with
(3) Square or six-sided emplacements, raised about 3 feet
above ground level. Walls (2 feet thick) of sand and sandbags
were contained by corrugated sheet iron, posts, and so forth. The
inside diameter was 10 feet; the exterior
diameter, 14 to 15 feet. (One gun was provided with
a 3/8-inch-thick steel shield.)
(4) Twin, eight-sided concrete emplacements, which were part of a
ground machine-gun and antiaircraft machine-gun casemate (already
described in par. 6a).
(5) Emplacements on top of buildings and revetments; these were
circular and simply constructed of sandbags.
c. Twin Mount
Two types of emplacements for the twin-mount guns were noted:
(1) Slightly pear-shaped emplacements, 10 feet across at the
rear and slightly less at the front; 3 feet high at the rear
and sloped forward to a height of 2 feet at the front; walls
made of sandbags 3 feet thick, and further banked by soft sand.
(2) Square emplacements atop ammunition magazine; 10 feet across
on the inside; walled by boards and banked with sandbags and loose
sand to a thickness of 3 to 4 feet; 2 feet high.
Figure 13 shows one of the three known types of pedestals for
the twin-mount machine gun.
|Figure 13.—Pedestal for Twin-mount Japanese 13-mm Machine Gun.|
8. FIELD GUNS AND EMPLACEMENTS
The location of emplacements for the three types of field guns
used by the Japanese on Betio indicates that their primary mission
was antiboat defense. Some of these guns—75-mm mountain
gun (Model 41), 70-mm battalion gun (Model 92),
and 37-mm rapid-fire gun (Model 94)—were
used as support weapons after our beachheads had been established.
Emplacements for all three guns were roughly of the same type. The
interior was arrow-shaped or, in a few cases, egg-shaped, with the
entrance in the broad end and the firing port in the narrow
end (see fig. 14). The walls consisted of a single layer
of logs, laid either horizontally or vertically. In some cases
they were lashed to retaining posts or were joined at the
corners with steel rod fasteners. The walls were
banked outside with mounds of sand, which were 4 to 5 feet in
width at the base.
|Figure 14.—Emplacement for Japanese Field Gun.|
Most of the emplacements were roofed with a single layer of logs, covered
to a depth of 2 to 2 1/2 feet by loose sand. A few
emplacements had no roofs (see fig. 15).
|Figure 15.—Open Emplacement for Japanese Field Gun (probably for 70-mm battalion gun).|
All emplacements had an unroofed entrance passageway in the rear, 5
to 6 feet wide and 5 to 10 feet long. In most cases the
passageway was curved so that a second rear wall could protect the
rear of the emplacement from blast or fire.
The firing ports of all emplacements except those on the northwest
coast were sheltered from blast and small-arms flanking fire by
means of log- and sand-banked wings. These were 5 to 8 feet
long and opened at an angle of about 100°. Some emplacements on
the beach were protected by low double-apron wire.
These emplacements, although obviously not designed for small-caliber
weapons, in many cases were used as last-ditch positions for riflemen
and machine gunners. In a few instances, the guns were removed
from the emplacements, turned around, and fired inland from the rear.
9. DUAL-PURPOSE GUN EMPLACEMENTS
a. For 75-mm, Model 88, AA Guns
Eight of these guns were emplaced on Betio. Four were sited as a
battery near the northwest corner of the island, and the other four
were arranged in pairs, one each on the north and south coasts of
the eastern tip.
Except for minor variations, all emplacements for the Model 88 were
similar. Dug to a depth of about 5 feet below the ground level, they
had five sides, which were revetted with empty oil drums and
with 1-inch-thick boards secured by vertical coconut logs
or by solid coconut-log walls. Ammunition ready-boxes of varying
sizes were built into one or more of the side walls. In some cases a
communication trench connected the emplacement and a nearby bomb-proof
coconut-log shelter. The revetments for all emplacements were higher
on the inshore sides than on the seaward sides, permitting low-angle
antiboat fire on beach approaches. Sandbags secured the fill on top
of the revetments.
The guns were mounted on spider-leg pedestal mounts.
Each group of guns was provided with fire-control equipment
consisting of a range finder with a 2-yard base
and a small (Model 1930) sound locator with four
horns. Searchlights (150-cm and 90-cm) were
located so as to serve both the antiaircraft and nearby
b. For 127-mm Twin-mount Guns
These guns, designed for coastal defense as well as antiaircraft
defense, were emplaced in pairs in two locations. Their
emplacements were constructed of concrete and were banked
from the ground level to the brim of the concrete parapet
with coral and sand. The distance between emplacements,
center-to-center, was 40 yards.
Spaced at equal intervals around the side of the parapet were 10
ready-boxes, each holding 12 rounds of ammunition. Ammunition
stores were kept in four concrete, sand-covered, bomb-proof
buildings in the vicinity. Apparently the ammunition was
carried from the main storage buildings to the ready-boxes.
A fire-control position for the battery of two twin mounts was
located on a sand-covered concrete structure, 30 feet square
and elevated 15 feet above the ground. A range and altitude finder
and a director were mounted on this. The electrical and
communication equipment for the installation was placed inside
this structure, which was protected by four 7.7-mm machine
guns placed at each of the four top corners. Additional protection
for the entire installation was provided by two
twin-mount 13-mm machine guns on top of the
ammunition storage structures on the flanks.
A 150-cm Model 1933 searchlight was located 100 yards out on
each flank of the installation.
10. COAST-DEFENSE GUNS
Japanese weapons on Betio emplaced solely for coast defense included
six 80-mm guns, four 140-mm guns, and
four 8-inch shielded naval type guns.
a. 80-mm Guns
These guns were found in batteries of three. There were two such
batteries, one located in the center of the west beach and the other
on the eastern part of the south shore. The latter battery had a
secondary mission of covering the south reef antitank barrier
with flanking fire.
The emplacements were constructed of logs and sand, and were open
at the top except for palm-branch canopies provided for camouflage. They
had six sides, with a rear entrance. Double walls, made of logs, formed
the six sides. Each log wall was laid horizontally, and was three logs,
or 3 feet, high. The space between the double walls was about 3 feet
and was filled with sand.
The front side of the emplacements paralleled the beach. Built into
the two rear walls were concrete ammunition shelters, each capable
of holding three ammunition boxes of 12 rounds.
Japanese standard-type bomb-proof shelters, each capable of
holding 12 men, were located to the rear and to one side of
An observation tower, 15 feet high and constructed of logs, stood
just behind, and to one side of, the central gun of each battery.
b. 140-mm Guns
Two of these weapons were located on the northwest point, and two
on the east point. They were mounted in circular concrete pits
which rested on the normal ground level. The floor parapet and
ready-boxes of each pit were made of reinforced concrete and
banked with sand. The pits, or emplacements, in each battery
were about 60 yards apart.
The fire-control arrangement for each pair of guns included an
observation tower, 80 feet high, which was erected on a
sand-covered, bomb-proof shelter. The latter housed a power
distribution board for supplying electricity to the guns and a
communication or control center for the battery.
c. 8-inch Shielded Guns
Four of these guns were found on Betio, two on the southwest
corner and two on the southeast coast.
The two guns on the southwest corner were mounted in a tandem
arrangement in concrete emplacements, which were banked all
around with sand and coral.
Ammunition was stored in a heavily constructed bomb-proof shelter,
75 yards from the gun position. A narrow-gauge railroad
track led from the storage shelter to an ammunition ready-room
which separated the two gun positions. Small hand-drawn cars were
used on the track.
The fire-control system for this installation included a plotting
room in a lower level of the upper gun emplacement, an observation
tower (70 feet high), and the necessary wire and voice-tube
communication between these elements and the guns.
The two guns on the southeast coast were located in circular concrete
emplacements about 10 feet above the ground. The two emplacements were
about 100 yards apart.
Ammunition and powder, and the personnel to handle them, were sheltered
in four magazines situated a few yards to the rear of each emplacement. A
ready ammunition-handling shack also was situated behind each emplacement.
A fire-control tower, 45 feet high, was situated behind the two guns.
The Japanese had 14 Model 2595 (1935) light tanks on Betio. They were
camouflaged in dug-in revetments, the tops of which were flush with
the ground. The camouflage generally consisted of palm leaves.
Nine of the tanks were held around the air-defense command post
near the lagoon shore.
12. COMMAND POSTS
The rifle and machine-gun positions, which formed the primary beach
defense, were controlled from steel pillbox-command posts, spaced at
intervals of about 300 yards around the perimeter of the island.
These pillboxes were prefabricated, six-sided, truncated pyramids with
double walls made of steel (see fig. 16). Both the outer and inner
plates were 1/4 inch thick, and the space between them was filled with
sand. In most cases the exterior of these pillboxes was banked with sand or
camouflaged with palm fronds.
|Figure 16.—Japanese Steel-pillbox Command Post (side view showing firing port).|
Inside, these pillboxes were divided into an upper and a lower
compartment. The upper compartment was designed for an observer
or commander. It had an observation seat, a voice tube, and a
hatch, which opened outwards from near the sides. The voice
tubes led down into the lower compartment, which apparently was
designed to house two machine guns. This compartment had two
large ports, one on the left flank and one on the right, and a
small peep sight to the front. The large ports were equipped
with bracket supports for machine guns, but apparently no machine
guns were used in any of the pillbox-command posts on Betio.
|Figure 17.—Japanese Steel-pillbox Command Post (upperrear view showing entrance; lowertop view looking down into hatch).|
One steel pillbox on the south beach was capped with 12 inches of
The largest reinforced concrete structure on the island was believed
to have been the main headquarters. It housed the terminal facilities
of radio and telephone equipment, as well as administrative
personnel. The reinforced concrete was very thick. The structure
was additionally protected by a thick layer of sand on the roof, on
which two 13-mm machine guns were emplaced. Apertures
were provided in the walls of the building for the firing of small
arms and light automatic weapons, but the primary purpose
of the building apparently was to provide shelter for
personnel and equipment.
The shelters found on Betio can be broadly divided into two groups: those
located in barracks and headquarters areas and those located to
Those in the barracks and headquarters areas were designed to
protect large groups of personnel during air or surface
bombardment. They were constructed of alternate layers of
coconut logs and coral sand. Side walls and roofs
averaged 5 to 7 feet in thickness. Ventilation shafts
were provided, but there were no gun or rifle ports.
Those in the beach-defense areas were designed and used, during
bombardment, as standby shelters for personnel who were
waiting to man beach positions. These shelters were smaller
and not as heavily constructed as those inland. They were
located immediately adjacent to defensive positions. Several
were constructed of reinforced concrete 12 to 16 inches
thick and covered with sand. Others were constructed of logs
and sand. They varied in size and design to suit the particular
needs of an area. Like the larger structures, the beach-defense
shelters were designed for protection, not as prepared defensive
|Figure 18. [click to enlarge]|
1 A short preliminary discussion of the Japanese defense
of Betio Island was carried in Intelligence Bulletin,
Vol. II, No. 6, pp. 19-38.