The vastness of the Pacific with its multitudinous small islands presents
many problems of defense. The following article is based on excerpts from a
translated Japanese tactical treatise involving a study of the dispositions to be
made for the defense of a hypothetical coral island. The study contemplates the
utilization of field fortifications when landing operations are threatened by an
enemy who is superior in air and sea power. There are many points which are
not covered in this article, but it is being published as it is, in the hope that it
will be of some value.
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The organization and establishment of positions differs depending on the
size of the island, the garrison's forces, weapons, and materiel, the situation of
beaches where it is possible for the enemy to land, and many other factors. However, in
case the strength of the garrison is comparatively small in relation
to the size of the island, if an attempt is made to defend the island by stationing
troops all around the shore line, the defense will be weak everywhere. Therefore,
it is best to organize defense areas at important places so as to hold securely the
important installations, with a large force being held in reserve. The intervals
between defense areas should be covered by fire and obstacles should be
constructed in these intervals. If necessary, small supporting points between the
main defensive areas may be occupied with a part of the forces.
For obstacles within the island, it is necessary to select types of obstacles
which will not show in aerial photographs so that the enemy cannot determine our
dispositions for defense.
The plan of defense should be to destroy the enemy at the water's edge,
but should he land, he will be annihilated by counterattacks.
b. Garrison of Defense Areas
The garrison of the defense areas differs, depending upon the mission,
the size of the area occupied, and other considerations. However, on a coral
island, ordinarily from one to two companies are necessary for the garrison of a
defense area. The frontage assigned varies according to the type, number, etc.
of the weapons which are to be located in the defense area, but if two platoons are
placed on the front line, one company would be able to hold a front of 550 meters*.
If the interval between platoons is covered by the coordinated fire of heavy machine
guns from the platoon areas (the interval between platoons being 500 to 600 meters),
the frontage assigned to a company may be about 1,000 meters. The depth is
about 150 meters for the platoon and about 400 meters for the company.
c. Method of Determining Frontage
The frontage assigned to the various units is determined by using density
of fire as the standard.
Density of fire required for stopping an attack dead -- 5 shots on one meter
of front every minute. Minimum limit of density of fire -- 3 shots on one meter
front every minute. (These include rifle, LMG, and MG).
Rate of fire -- rifle (10 shots per minute)
-- LMG (150 shots per minute)
The heavy machine gun is used for flank defense. On the front, rifles,
LMGs, etc., are used according to a fixed plan, or to fire at will on important
targets. The degree of density, however, in each sector is not calculated.
(2) Frontages Covered by Various Units
(a) Squad front covered = 50 to 90 meters
11 rifles firing 10 rounds per minute = 110 rounds per minute
1 LMG firing 150 rounds per minute = 150 rounds per minute
Total = 260 rounds per minute
260 divided by 5 shots per meter per minute = 50 meters
260 divided by 3 shots per meter per minute = 90 meters
Therefore, 50 to 90 meters frontage.
(b) Platoon front covered = 200 to 300 meters
3 rifle squads on front line - 50 x 3 = 150 meters
90 x 3 = 270 meters
With heavy grenade squads on front line = 200 to 300 meters
(c) Company front covered = 400 to 600 meters
Two platoons on front line - 200 x 2 = 400 meters
300 x 2 = 600 meters
Therefore, 400 to 600 meters frontage.
(d) Battalion front covered = 800 to 1,800 meters
2 companies on the front line -
400-600 meters x 2 = 800 to 1,200 meters
3 companies on the front line -
400-600 meters x 3 = 1,200 to 1,800 meters
Therefore, 800 to 1,800 meters frontage.
d. Frontage Depending on Degree of Deployment
(1) Front occupied by squad--about 35 meters:
Interval between men in deployment is 6 paces (about 4 to 5 meters). In
building earthworks the interval between the fox holes of the riflemen is about 3
to 4 meters, and as one squad has about 10 men, one squad's frontage is 30 to 40
(2) Interval between squads--normally about 65 meters:
The frontage which one artillery battery can cover with an even density of
fire is about 100 meters, so it cannot support two squads. Therefore, if the
squad's front is 35 meters, the interval between squads should be about 65 meters.
In such a situation, it is necessary to consider laying down barrages in the
intervals between the squads by the artillery in the rear.
(3) Distance between the squad in a platoon position--about 100 meters:
The distance should be about 100 meters for the same reasons as those
given in the preceding paragraph.
(4) Area occupied by the platoon (see figure 1.)
The area occupied by the platoon has a frontage of approximately 230
meters and a depth of approximately 100 meters. The depth may be greater
depending on the position of the platoon leader, the location of the heavy weapons,
(5) Area occupied by the company (see figure 2.)
The area occupied by the company has a frontage of approximately 550
meters and a depth of approximately 400 meters.
(6) Area occupied by the company when a wide front is assigned and the
interval between the front line platoons is covered by machine guns
(see figure 3.)
When there is a wide company front and the interval between the front line
platoons is covered by machine guns the company frontage will be approximately
1,000 meters and the depth approximately 400 meters.
(7) Area occupied by the battalion (see figure 4.)
With two companies in the front line the area occupied by the battalion
will have a frontage of 1,200 to 1,400 meters and a depth of approximately 1,100
When there are three companies in the front line the battalion area will
have a frontage of 1,800 to 2,200 meters and a depth of approximately 1,100
In the above, a standard has been sought, but in actual practice, circumstances
will vary so much that it is not possible to follow this standard rigidly. In
case there is much dead space, the capabilities of the weapons cannot be fully
utilized and the frontage is very much reduced. In the case of firing over water
as in coastal defense, the frontage can be increased up to the limit of easy
The reserves should be stationed at a point from which it is easy to move
them up to reinforce the front line, or to counterattack, as required by the
situation. On coral islands, there is little space in which to maneuver for a
counterattack, so in many cases counterattacks must be made frontally. Therefore, it is
very advantageous to have tanks, armored cars, and so on, available.
Furthermore, as the enemy has planned to use amphibious tanks in
landing, it is necessary to have material ready for close-quarter antitank attacks.
f. Interval Between Defense Areas
The interval between defense areas will vary with the type of weapons
used to cover these intervals. In case machine guns are to cover the space with
cross-fire from both sides, the interval is approximately 600 meters; in case
machine guns from each side cover one half of the ground, it may be about 1,000
meters. When covered by artillery fire, the interval may be from 2,000 to 4,000
However, against coastal defenses, the enemy often tries surprise night
attacks, so the interval between defense areas must be decreased and the defenders
must endeavor to destroy the enemy at the water's edge. Therefore, the ability of
the machine gun to cover the interval should be the limiting factor for the size of
the interval, and it should not be extended much beyond 1,000 meters.
The enemy's landing must be prevented by blocking the intervals between
defense areas with obstacles as well as by covering it with fire. Wire
entanglements are commonly used as obstacles, and in areas where it would be easiest
for the enemy to land, wire entanglements and land mines are used together.
Charged wire entanglements can be used effectively.
In case an interval between defense areas is very great, it is necessary
to close the gap by organizing small support areas between the defense areas.
g. Location of Machine Guns
The essential points to be considered in emplacing machine guns to deliver
flanking fire are as follows:
(1) Locate machine guns to be used to deliver flanking fire upon the
attackers so that it cannot be seen from the front, in a covered position if necessary,
and so that the loophole cannot be fired on, thus preventing the enemy from
advancing upon the position.
(2) Covered machine-gun positions whose loopholes can easily be seen
and which are destroyed early are of no value. In such cases, it is best to place
the machine gun in an open emplacement in a rifle position.
h. Disposition of Artillery, AA Guns and Other Equipment
The heavy and medium caliber guns are chiefly used in shelling the ships
covering the enemy's landing, the transports, etc., and the small caliber guns are
to destroy the enemy's landing boats while off shore or, when he lands, to
cooperate in the fight at the water's edge. They also have the duty of engaging the
enemy's tanks. Usually the heavy and medium caliber guns are placed at the
most important points, and the small caliber guns are distributed among the
defense areas. All of these guns must be fully protected by the infantry in the
defensive areas. The small caliber guns, however, when necessary, may occupy
positions outside defense areas, or a part of them may be held in reserve.
It is essential that other important equipment also be placed within the
defense areas and thoroughly protected.
i. Location of Observation Posts
Since the enemy plans to approach at high speed at night with highly
maneuverable ships to make a surprise landing, it is necessary to keep an especially
strict guard to avoid being surprised. To this end it is necessary that the
observation net be organized so that important areas can be observed from several
directions and so that even the comparatively unimportant areas will not be
j. Measures to be Taken Against Bombing and Shelling from Enemy Ships
Coral islands are generally level and it is difficult to utilize the terrain
for the protection and concealment of positions and installations. It is most
necessary to use camouflage to conceal the positions and the disposition of weapons,
etc., and to use dispersal to limit damage. Of course, it is to be expected that
there will be strong, permanent installations built to stand up under shelling and
bombing, but these cannot be built to meet an emergency. Ones which are strong
enough to be proof from bullets and shell fragments may be considered
advantageous. Furthermore, the heavy weapons, etc., used for flank defense should have
light covers; the other weapons should be uncovered, and completely camouflaged.
At the same time reserve positions should be established and, emplacements for
the weapons should be constructed near the position to prevent damage during
shellings and bombing.
*To convert meters to yards add roughly 10 percent to the number of meters.