When forced on the defensive the Japanese have striven to attain the
element of surprise by means of silence and concealment; employed deceptive
measures wherever possible; made extensive use of snipers; and attempted to
disrupt the enemy advance by infiltration tactics. The following data on
Japanese defensive tactics is taken from a recent British publication.
* * *
Unless attacked, Japanese troops occupying forward positions very seldom
open fire, for fear of disclosing their location, even if the target offered
is a good one. From the Japanese point of view, the defensive battle begins
only when the assaulting troops are too close to be missed by their light
and heavy machine guns. Carefully-concealed machine-gun positions then come
to life when the assaulting troops are too close to the objective to receive
support from their own artillery. If the assault is up hill the Japanese add
showers of grenades.
Following normal practice the Japanese make the machine gun the principal weapon of
defense. Automatic weapons are sited to fire along prepared lines, lanes being cut
in the jungle if necessary. Heavy machine guns are sited well forward and are generally
sub-allotted to platoon areas; they are often to be found on high ground or dug into the
banks of "tanks," (water reservoirs); they are also sited to cover the main lines of
approach; they are often placed singly, and frequently alternative positions are
provided. An important point to remember is that during the defensive battle heavy
machine guns sometimes fire along a line not more than ten yards from the forward
edge of the Japanese main line of resistance, and assaulting troops, if unprotected by
smoke or darkness, may therefore suffer heavy casualties just in front of the enemy
position, particularly if they have become bunched in converging on the objective. Mortars
and grenade dischargers come next in importance to the machine gun. Mortars of 3-inch or
larger caliber may be allotted to rifle companies at the scale of one per company, but
the weapon most frequently used by forward units is the 2-inch grenade discharger of
which there are three in each platoon. This weapon throws a heavy grenade 700 yards. Once
an attack is launched mortar and grenade discharger shelling is frequently directed
on areas which cannot be reached by flat trajectory weapons. Particular
attention is paid to probable lines of approach and likely assembly areas.
Although the extent to which snipers are employed varies greatly with each
front, there are certain places where snipers may be expected; namely, above
small advanced positions, on the flanks of defense areas, covering lines of
approach to Japanese positions, and covering paths in our own [British] area. Patrols, varying
in strength, are very active at night and attempt to infiltrate between positions held by
our troops - particularly those new to a sector.
The Japanese, so far, have made little use of artillery in defense. They tunnel into
hill sides and build dugouts which afford adequate protection against all but a direct
hit from a field gun. Well-built enemy earthworks often render his destruction by the
normal supporting weapons impossible. Supporting fire shakes him and makes him keep his
head down, but if the assault does not go in with all possible speed after the supporting
fire has lifted, he is quick to seize the momentary advantage which slow troops may give him.
The Japanese launch immediate counterattacks against troops who have captured
part of a position. These small local counterattacks may be made by only a dozen
men led by an officer; they are preceded by a shower of grenades from grenade
dischargers and the charge is made with automatic weapons. This immediate counterattack
may be launched five to ten minutes after the position has been penetrated. A wild
war cry, to which is sometimes added the shout "Charge!" in English, gives warning
of what is impending.
Two examples of the Japanese conduct of the defense, are illustrative of most of the
tactics commonly employed.
a. Example 1
In one case the Japanese placed a forward defense area on the hill illustrated in the accompanying
sketch. All earthworks were carefully camouflaged and had it not been for sentries in our own forward
positions, about 50 yards down the left slope of the hill, hearing the Japanese talk at night, it would
not have been possible to say definitely that they were there.
Our reconnaissance parties, exposing themselves boldly on a ridge facing this position and 400 yards
from it, were never fired upon, and many rounds of 3-inch mortar bombs were fired into it without
producing any reaction.
The general line A-B was nearest to the point of observation. The position, however, continued
on the right of A following the high ground which curved back slightly. It also receded
behind B following the highest contour.
The position around A-B was probably held by a platoon as part of a company holding the main
hill of which this feature was only a part.
The information available to the attacking troops, was that there were some
enemy on the hill who had never been seen. They had been heard to talk at night
and were believed to consist, at the very outside, of one platoon.
After an intensive mortar bombardment one company launched an attack up both
sides of the spur from C. The black arrows indicate approximately the line of
advance of the main assaulting parties.
The leading assaulting troops made good progress until they were about 30 yards from the general
line A-B; then a veritable hurricane of fire was let loose upon them. They were engaged by light
machine-gun and grenade-discharger fire and began for the first time to suffer appreciable
casualties. Shouting their war cries they continued to climb the hill, making use of such
meager cover as the small bushes and folds in the ground offered. As the action grew in
intensity camouflage began to slip off the parapet of what could now be identified as a
continuous trench, part of which ran along the front A-B. When the leading troops were
about ten yards from the parapet, they were subjected to accurate Japanese heavy machine-gun
fire from a gun sited in another position. Although greatly weakened by
casualties, they, the [British] continued to advance and, led by their company
commander, hurled grenade after grenade into the Japanese position. They finally
stormed and occupied the trench, killing or driving out all Japanese in that sector.
About ten minutes later there was a wild howl, as of jackals and hyenas; a shower of
grenades from grenade dischargers fell among our troops, and with shouts of "Charge!" the
Japanese counterattacked with automatic weapons, forcing our troops off the hill.
Comment: This company battle serves as a vivid example of Japanese methods in
the defense. Their positions were well concealed and nothing tempted them to give them
away; thus at zero hour, the attackers could be certain neither of the extent of the
position nor the strength in which it was held. They had heard Japanese talking in
this area at night and with the Japanese predilection for occupying commanding
ground, they could reasonably be expected to have organized a position there.
Fire was held until the attackers were 30 yards or less away, and not
until 10 yards from the parapet were they engaged by heavy machine-gun
fire from a nearby position. This is a common Japanese method of achieving
surprise in the defense.
Finally, the successful assault, which was not reinforced, was turned to failure by a
small but determined local counterattack. The immediate counterattack is a common, though
not invariable Japanese maneuver. There have been cases in which captured positions
have been made untenable by fire alone.
b. Example 2
In another instance, an attack against a strong Japanese defensive position in Burma was made.
(1) Plan of British Attack
The plan of attack was divided into four phases:
Phase 1--At 0545 A Battalion to capture the eastern half of the
Chaung River as far west as M16 (see accompanying sketch).
Phase 2--At 0645 B Battalion to capture the jungle area as far as line marked "A."
Phase 3--At 0710 C Battalion to extend their position on Twin Knobs to as
far south as the line marked "B."
Phase 4--At 0850 B Battalion to exploit to line marked "C."
Artillery and heavy machine guns supported the attack with a barrage and concentrations.
(2) Japanese Position
The Chaung itself is a strong, natural obstacle, which the Japanese made into an excellent
defensive position, by building an intricate system of communicating weapon pits and defense
areas, and at least one pillbox at S5 (see accompanying sketch). All positions were mutually
The pillbox or bunker, which consisted of an outer covered weapon pit, and an inner chamber
which is reported to have included both metal and concrete materials, was sufficiently well
built to withstand no less than three direct hits from a 3.7-inch howitzer at point-blank
range. It follows, therefore, that assaulting troops on and around the pillbox could be
subjected to heavy mortar fire without any detrimental effects to the occupants.
All other works were dug well down and presumably provided with dugouts, for
although approximately 124 tons of shell were fired into the Chaung area immediately
prior to the attack, there was no indication that the enemy's fire power had been impaired.
The Chaung is overlooked from the east by two commanding positions, Hills 823 and 500. These
are both steep and densely wooded. Although no weapons were pin-pointed on these hills, mortars, heavy
machine guns and at least two 75-mm mountain guns undoubtedly fired from there. These weapons
could thus put down defensive fire anywhere in the area, by day, by night, or through smoke.
Unlike other Japanese defensive positions, weapon pits and fox holes near the Chaung were
clearly visible from the air and in many cases could be seen from OP's. This does not
mean that any movement, or guns were visible, but it was possible to determine where
earthworks had been dug. However, in the jungle and on the hills 823 and 500 positions
were so well concealed that with the exception of the two strong points which held
up B and C Battalions, they remained undiscovered to the end of the battle.
(3) Course of the Battle
A Battalion commenced their advance without appreciable opposition, but soon the
company attacking the Chaung from the north experienced the now familiar Japanese
tactics of withholding their fire until the last moment, and it was not until they
were crossing low, loose strands of wire, about 15 yards from bunkers at S4 and
S5 (see sketch) that intense fire was brought to bear on them. These two bunkers
were attacked repeatedly, but without success; our troops could find no opening
through which to throw grenades and while on and about these bunkers they were
subjected to mortar fire to which the bunkers themselves were immune. The other
two companies were more fortunate, and although they were subjected to showers of
grenades from grenade dischargers and hand grenades while advancing down the Chaung, succeeded
in taking their objective, which included M16. A proportion of these troops advanced
up the small Chaung and cleared it as far as S4 where they in their turn were held up. As
the light improved, and as presumably the Japanese realized the situation, showers of
projectiles from all weapons were fired into and around the Chaung, and heavy machine
guns opened up from the flanks.
Meanwhile Phase 2 began and B Battalion advanced only to be held up by what was
described as a defense area similar to S5 (M52 on the sketch). B Battalion was
unable to reduce this position and was subsequently withdrawn.
Phase 3 commenced according to plan, but C Battalion almost immediately suffered the
same experience as B Battalion, in that they ran into a cunningly concealed heavy
machine gun position just beyond the line of departure. This position was so well
hidden, that it escaped notice when the area was reconnoitered prior to the
attack. This position also held out.
Comment: The attack failed through no lack of courage; the dash
and daring of the attackers has been aptly described as an epic of collective
gallantry. Why then did the defense succeed? There are important reasons:
Following his normal practice the Japanese held his fire until the assaulting
troops were almost upon him; only then did his machine gun nests come to life--machine
gun nests about whose strength or existence we knew little or nothing. To quote
from a British defense pamphlet the main task of medium [U.S. heavy] machine
guns. . . will be to take toll of enemy unarmored troops. . ." and
no heavy machine gun is better sited to fulfill this role than one in an undetected
nest with a big enough covering of earth, timber, and perhaps steel and concrete, to
withstand the preliminary bombardment. In fact, by continually improving their positions
and by careful attention to camouflage, the enemy had achieved surprise in the defense.
Strong positions which could withstand the fire of our artillery could also
withstand the fire of Japanese mortars which gave additional protection to their garrisons.
The first and chief problem then, which the Japanese defensive position presents, is the
problem which has faced every modern army for more than 25 years--it is the detection and
neutralization of the machine gun firing from a well-built nest.
It will be noticed that no counterattack was launched in this battle, elements which
had penetrated the position being dealt with by intensive mortar and grenade-discharger
fire alone. This practice of bringing down defensive fire on one's own positions is
likely to be a common feature of Japanese defensive tactics. In fact either by immediate
fire or immediate counterattack the Japanese will attempt to make an overrun position untenable.
* * *
American Observers' Notes
Officers just back from the New Guinea and Munda fronts describe a Japanese
defense system containing rather unusual features.
The area to be covered is fortified with bunkers set as closely as five yards
apart with a second line of bunkers covering the gaps and a third line behind
the second. The bunkers themselves are made of three layers of springy palm logs
covered with earth and skillfully camouflaged. So strong are they that one officer
reported he had seen British 25-pounder shells and our own 81-mm mortar
projectiles "bounce off them." A 105-mm howitzer shell, however, would
penetrate (see accompanying photographs for typical bunkers.)
Behind the lines of bunkers the Japanese sited mortars.
The armament of individual bunkers was apt to be an automatic weapon, which the Japs operated until killed.
Instead of fire-lanes, passages about 2 feet square were cut through the brush or grass, down
which the Japanese would fire. Such rabbit-runs were practically impossible to detect until
the garrison of the bunker opened fire.
Frequently, bunkers would be protected on each side by rifle pits, connected to the
bunker by a shallow crawl trench. Access to the bunker was by holes so small an average
American could not wiggle through. "The Japs," stated the observer, "burrowed like gophers."
Another favorite defense was to dig in among the roots of a banyan tree--a large tree
that stands up above the ground on a mass of stilt-like legs.
Canister fired by a 37-mm gun proved effective against such a defense. Its balls
tore through the jungle growth for 150 yards, delivering a cone of fire about 30 yards
wide at 100 yards range, sufficient to hit both the bunkers and its protecting
riflemen with the same charge.
The bunkers shown in the accompanying photographs, were part of a Japanese defensive
position in New Guinea. It is reported that they were thoroughly "worked over" with
artillery before their capture, which may account for the lack of camouflage. The
timber in this case is probably cocoanut logs. Elsewhere a type of palmetto is
used. Both woods are springy and therefore tend to absorb the shock on contact
of a shell. In the first photograph note how close the bunker in the background
is to the one in the foreground. It was this type of Japanese field fortification
that has caused U.S. troops such difficulty in the Munda area.