Japanese Jungle Warfare, Intelligence Bulletin, April 1944 (Lone Sentry)

1. INTRODUCTION

The following information on Japanese jungle warfare is largely based on enemy sources, all of which are believed reliable. Most of the information was disseminated by the enemy after he had suffered numerous reverses in the Southwest Pacific, and therefore should include some of the latest tactics he has devised for jungle combat.

This discussion of Japanese jungle warfare is not intended as a complete study of enemy tactical doctrine on the subject. It deals largely with information which has not previously been widely disseminated among U.S. troops. For a more complete study of enemy jungle tactics, reference should be made to the first 12 issues of the Intelligence Bulletin (Vol. I), all of which include information on the subject.

2. GENERAL

According to the Japanese, their "reverses" in and around Wau, New Guinea, were caused by insufficient rations, inexperience in jungle movements, and unfamiliarity with the terrain. Blame for many of the shortcomings in this and other unsuccessful South Pacific campaigns was placed on junior officers and noncommissioned officers.

Discussing the plans of United Nations forces, a Japanese source points out that "everything hostile forces do has a meaning; no matter how small the details, each is a part of a plan. Therefore, it is important that we observe such things at once. If we fail, we will be taken in by the opposing forces."

"When we perceive these details," the Japanese treatise continues, "we must next decide on plans to counter the opposition, and take advantage of weaknesses.... If you keep studying your opposition, no matter how small and insignificant the information may appear to be, you will improve your judgment for use during critical moments."

a. Training

Japanese notes on training stipulated that:

(1) Battle regulations be read until they were memorized by all personnel.

(2) Officers thoroughly instruct their men on enemy weapons, uniforms, and features (they should at least be able to identify an automatic rifle by its sound).

(3) The ability of troops to throw hand grenades be improved.

(4) Training be given in climbing and descending cliffs by means of ropes (this applies particularly to heavy-weapons units).

(5) Further training be given in the transmission of orders. (It is necessary to insure accuracy in this phase of warfare. If circumstances permit, it is best to write out orders before they are transmitted.)

b. Disposal of Booby Traps

The Japanese look for booby traps in areas where United Nations forces expect the former to pass, or in areas the Japs might pass over to avoid booby traps.

If a booby trap is discovered, the Japanese search the area thereabouts for others. The first unit passing through a booby-trapped area should remove the traps, according to enemy instructions.

c. Equipment

A Japanese report on jungle equipment stated that leather shoes should be worn because rubber-soled shoes caused soldiers to slip easily. The report included the following additional points:

(1) Uniforms should be dark green.

(2) Each section should be furnished two automatic rifles similar to those used by U.S. forces.

(3) Each company should have two guns of a type between a grenade thrower and a rifle.

(4) It is necessary to have field guns (100-mm howitzers, if possible). Hostile field pieces have been very successful, and we have had no really effective answer. If we had field guns with us, the hostile artillery positions could be neutralized.

(5) Comparatively speaking, our grenade throwers are inferior to those used by United Nations forces.

(6) There have been times when our hand grenades misfired because they were damp.

d. Care of Wounded

The Japanese "very much regretted" that it was necessary to leave the wounded behind in the Wau operations. "In the future we will give further attention to arrangements for rescuing the wounded. However, if the wounded cannot be rescued, they must be ready to commit suicide at the proper time—that is, after all means to continue the fight have been exhausted.

"In case the wounded are retiring to the rear, always let them carry their small arms and equipment. Their ammunition should be left with comrades at the front. It is regrettable that there have been numerous instances of wounded men abandoning their weapons on the battlefield. Also, there have been instances of men leaving the front line without permission immediately after suffering wounds. This is prohibited."

3. OFFENSE

a. Movement

During movement in the jungle, Japanese combat forces usually are preceded by a road-repair section, which clears obstacles and takes other possible steps to facilitate travel. In mountainous terrain, this section hangs ropes, erects steps, and constructs guards to prevent troops from slipping.

The force commander usually distributes radios at intervals in the column during the march, to keep himself informed about the situation.

Because the heavy-weapons unit moves more slowly than other units in the column, a Japanese regimental commander suggests that it travel independently in a separate column. In the rugged terrain of the Wau area, the rate of march of an enemy heavy-weapons unit was only about 4 miles per day, alternating 20 minutes of marching with 20 minutes of rest.

The Japanese regimental commander recommends that, during marches in the jungle, bivouacking be done in march formation along the road. However, he adds, the force in the column must shorten its distance to the front. Seldom are there places where the force may assemble together.

The force should go into bivouac 1 1/2 to 2 hours before darkness and should leave about 1 hour after dawn, according to the regimental commander.

To aid their movement at night, a Japanese unit on Bougainville Island marked a trail with vines which had been tipped with phosphorus.

b. Combat Methods

(1) Launching the Attack.—The following notes on Japanese combat methods were paraphrased from enemy sources:

In the jungle, dawn and dusk are considered the best times to launch an attack, especially if it is raining. Under such conditions the hostile forces are under tents in trenches, and therefore it is easier for us to approach undetected.

Gaps between hostile positions are comparatively wide (75 to 100 yards), and in many cases they are poorly guarded—sometimes not at all. Therefore getting into these positions is a simple matter.

It is bad tactics to concentrate on, or be diverted to, the front of the hostile forces. It is usually best to employ a small part of your force to make a frontal attack and use your main forces to attack the rear and flanks of the opposition.

When a frontal attack is employed, it is necessary to make thorough preparations. The plan of attack must call for the most effective use of the various heavy weapons and for full use of artillery. Because the terrain is generally wooded and affords a limited field of fire, it is easy to conceal our movements while assault preparations are being made. The depth of hostile defense positions does not exceed 650 yards during the first stages of combat. The curtain of fire at the front of these positions is heavy, but from there to the rear it thins out. Hence it is advisable to make a bold, decisive breakthrough at once.

After launching a frontal attack in a wooded area, it may be advantageous to shift the main force to the rear and flanks of the opposition. This method is particularly good against forces defending a defile along the beaches.

If hostile forces unexpectedly fire on you in the jungles or on grassy plains, do not become excited and return the fire. You must guard particularly against making noises. If you are in position under a unified command, the commanding officer will be prepared to take offensive action against the opposing forces.

You must be continuously on the lookout for hostile observers and snipers, and pick them off with carefully aimed shots. Where their presence is suspected, spray the trees with machine-gun fire.

In New Guinea we used our light machine guns too liberally, and suffered a relatively large number of casualties among the machine gunners. Riflemen should be used to search out the hostile positions, while the light machine guns should be reserved for definite targets.

If our positions are discovered by hostile mortar fire, we must change positions immediately, first retreating about 100 yards.

The power of hostile forces can be effectively reduced by cutting off their supplies—this breaks their fighting spirit. Therefore, at every opportunity, launch surprise attacks in the rear for this purpose.

Our soldiers must rely on their bayonets. U.S. troops depend too much on their fire power and lack the will to fight, both physically and spiritually. Therefore, have confidence in your bayonet, and lunge at your foe. In bayonet drill, practice the straight lunge, with your right foot well forward, so that the bayonet will penetrate all the way to its guard.

(2) Enemy "Rules" for the Attack.—The following Japanese combat "rules" were extracted from an enemy manual:

(a) Take advantage of semidarkness as well as of bad weather.

(b) If you encounter hostile forces unexpectedly, take the initiative and fire without hesitation.

(c) If you are in an exposed area of the jungle, find something with which to conceal yourself, instead of dashing around.

(d) Hold out until the end, because your foe will not rush you. However, be careful of his fire power and hand grenades.

(e) Always use the assistance of others instead of fighting alone. Make contact with your own troops in every possible way.

(3) Tactics Observed in Burma.—Just before certain attacks in the Burma theater, the Japanese reserve forces screamed and yelled. Their forward troops soon joined in the noise-making. Observers said such tactics were obviously designed to break the morale of the defending forces, to bolster Japanese morale, or to make it appear that the attacking troops were numerically stronger than they actually were.

The Japanese apparently made definite plans to concentrate their attacks in particular sectors, because they continued to press the attacks regardless of casualties or the strength of the opposing forces. Meanwhile, the enemy sent small parties to determine the location of the opposing flanks, with the possible intention of causing United Nations commanders to pull troops from front sectors to strengthen their flanks. Regardless of these maneuvers, the Japanese always concentrated on the attack sector previously selected, and tried to overwhelm the opposition by weight of numbers.

Besides probing fire, the Japanese have used two other methods to tempt United Nations forces to fire and give away their positions:

(a) Japanese soldiers, each equipped with a length of rope, tied the latter to bushes and then moved to a place of safety. Then they worked the rope in an effort to make opposing forces believe that enemy troops were moving among the bushes.

(b) Enemy soldiers employed a simple mechanical device to represent the clicking of rifle bolts. The device in each case was attached to a bush and connected by a rope to a soldier hidden in a place of safety. By manipulating the rope, he made the device sound like the operation of a rifle bolt.

c. Reaction to Ambush

Observers state that, as a general rule, the Japanese in the Burma theater have reacted in the following manner to ambushes:

Leading enemy elements got off the road or trail and sought to outflank the opposing forces. Then the Japanese opened up immediately with mortars (they are seldom without them) and attacked, astride the road or trail, the area in which the ambush was laid.

When ambushed, some Japanese soldiers have been known to fall and feign death.

d. Special Assault Units

In the South Pacific theaters of operation, the Japanese have employed several types of special assault units. In most cases they were not specially trained troops but combined units—or parts of units—selected to accomplish special missions, such as raiding lines of communication or artillery positions.¹ Some of these specially organized units were instructed to withdraw after accomplishing their mission, while others were designated as "suicide units."

The organization and mission of two of the "suicide units" in New Guinea operations were described in Japanese reports, which are paraphrased below.

One assault unit, commanded by a lieutenant, consisted of an infantry company and a detachment of engineers. This unit was to "advance within close range of the enemy's main position and attack." The engineers, acting as a demolition detail, were to carry Bangalore torpedoes "to destroy all obstacles and mop up within the positions." Two "suicide raiding units" of six men each were assigned to "penetrate No. 2 and No. 3 enemy positions," and to assist the main assault unit by "throwing the enemy's rear into confusion."

To assist in the operations, a second company was to act as a decoy, while another company was to advance closely behind the assault unit and "leapfrog" the latter at the appropriate time.

The assault unit was organized as follows:

Headquarters, 4 men; Assault Detail, 15 men; Obstacle Detail (1 platoon engrs.) ; Artillery-demolition Detail, 6 men; Raiding Detail, 7 men; Supporting Detail, 22 men; Reserve Detail, 32 men; Mopping-up Detail, 33 men.

The Assault Detail consisted of four "Grenade Groups," while the Supporting Detail had one light machine-gun squad and one grenade-thrower squad. The Reserve Detail included a rifle squad, a light machine-gun squad, and a grenade-thrower squad.

The second assault unit described by the Japanese, also led by a lieutenant, consisted of infantry and engineer troops. Its mission was to attack a U.S. coastal base from the sea. The enemy order covering the operation included the following:

The strength of the unit will be divided into two sections, combining infantry and engineer troops. There must be close coordination between the attacks by the infantry and the demolitions carried out by the engineer troops.

Equipment will be as light as possible. In addition to the necessary ammunition, carry as many grenades as you can.

The landing beach will be indicated under a separate order. Your objectives should be ammunition dumps, artillery positions, tanks, enemy headquarters, moored boats, barracks, and so forth.

The boat unit will return as soon as the assault unit has landed.

The attack must be completed before daybreak.

After the attack, the commander of the assault unit will use his own initiative as to whether he will concentrate his forces within the position penetrated or concentrate outside the position. However, he must be situated so that he can support the main regimental attack.²

4. DEFENSE

a. Organization of Positions

(1) Real.—Figure 4 is an exact tracing of a Japanese drawing to illustrate the organization of a defensive squad position. This set-up apparently was designed after the "Wau operations" in New Guinea. According to the drawing, emplacements for three to five men are constructed at each point of the triangle (a Japanese rifle squad is approximately the same size as ours). The distance between each group depends on the density of the jungle; however, groups must be within sight of each other. Each group of men is well equipped with hand grenades. The squad leader stays in whichever group is most convenient. "It is best," declares a Japanese source, "to connect communication trenches between the two groups. If one of the groups is attacked by hostile forces, the other groups will attack the rear flanks of these forces. If the latter penetrate to the center of the position, you will use enveloping fire."

[Figure 4. Japanese Squad Position (defense).]
(A) 3 to 5 men with hand grenades
(B) Distance between positions
depends on density of jungle
Figure 4. Japanese Squad Position (defense).

(2) Dummy.—A Japanese source states that "we have used various devices for constructing dummy positions and personnel, and also for firing from unexpected directions. Everyone should keep planning these day by day."

The enemy apparently is particularly interested in luring U.S. artillery to fire on dummy targets. In this connection, a paraphrased Japanese treatise reads:

Experiments conducted during the fighting at Munda proved that suitably prepared dummy positions and dummy guns were extremely effective in drawing hostile artillery and bombing attacks. In accordance with these results, always try to build dummy gun positions some distance away from our real positions.

Another method of drawing hostile artillery fire is to send out patrols to light fires. The smoke from these will certainly tend to bring down artillery fire on the area. This patrol must be led by an officer because the site must be selected with great care to prevent the hostile fire from reaching real positions.

[NOTE.—Since the Japanese repeatedly give strict warnings against the lighting of fires, smoke columns should be viewed with suspicion.]

A U.S. observer in a Southwest Pacific area described a dummy gun position and several dummy antiaircraft positions. The dummy gun was a coconut-palm log painted gray, with one end hollowed out to represent the muzzle. From a distance of 100 yards it appeared real.

Dummy soldiers were found at the antiaircraft positions. They consisted of tree limbs nailed together, with coconuts used as heads and Japanese uniforms used for clothing. The dummy antiaircraft guns consisted of tree trunks or limbs tied together. A large limb represented the receiver and a smaller one represented the barrel. It is doubtful if these positions would have deceived ground troops at a distance of 200 yards or less.

b. Plans to Counter U.S. Tactics

(1) Action Against Patrols.—In New Guinea, Japanese troops were ordered not to answer the searching-fire of hostile patrols. "One way to annul their intention (they seek to locate your positions) is to have snipers shoot the patrol," the order read. "Another method is to hide quietly, remain motionless until the patrol passes, and then knock the hostile troops out with one blow."

(2) Action against Ground Attacks.—The following information on Japanese tactics designed to counter U.S. offensive power is paraphrased from enemy sources:

Hostile attacks in a wooded area will usually begin with automatic rifle fire; the effective range is about 50 yards. Therefore, we can neutralize this fire by clearing a 50-yard area in front of our positions.

In wooded areas there have been instances of hostile forces attacking at close quarters. Troops must not neglect to guard all directions at all times; we cannot always depend on patrols. There have been instances in which patrols were lost in wooded areas and could not report at the proper time. Do not send them out too far; limit their area and give them a specific mission, so that they can be recalled at a suitable time.

__________

While standing guard, do not move your head quickly, otherwise you will often be detected. Make a hole in a big leaf and stand behind it, or construct a cover.

When cool firing is difficult due to heavy hostile automatic-weapons fire, there are many occasions when hand grenades will prove effective in carrying on the fight.

When hostile forces begin to retreat, the men on guard will increase their fire power and will launch a counterattack to destroy the opposition. However, take precautions to see that the men do not lose their way back.

Guards will entice small hostile forces to approach as close as possible and then destroy them. When somewhat larger forces attack, you must commence firing outside of grenade- throwing range (50 yards).

__________

The hostile forces [U.S. troops] do not possess very effective strength in the assault, but they will try to annihilate us by relying on fire power alone; therefore we will be wiped out if we try to defend ourselves while remaining in one place.

When hostile forces attack, we must act quickly in a minimum of time and confuse them by destroying the attacking unit. In using this method, we must preserve our strength instead of displaying it all on the front line. When we attack, the rear flank of the opposition will be the objective.

__________

The hostile forces are skilled in approaching by crawling, and they often get within 15 yards of our troops without being detected. They open surprise fire with very rapid-firing automatic weapons and deal destructive blows. However, they do not charge; their grenade throwers approach and toss grenades or shoot them with grenade rifles. If our positions are held strongly, the opposing forces will retreat after a short time, or they may send combat details around our flanks to attack with grenades and automatic weapons.

In taking countermeasures against such hostile attacks, we must scatter the opposing forces and then carry out a strong assault at one point. It is usually advantageous to attack the hostile flanks with two or three squads. Draw the opposition close by remaining under complete cover. Then, by surprise and accurate fire, kill the light machine-gun operator. However small your force may be, prepare to fight on all sides, and try to envelop any hostile envelopment by concerted action.

Clear away the underbrush for a distance of 15 yards from your positions; remove no more underbrush than necessary so that the clearing will not be noticeable.

__________

Hostile forces seldom, if ever, attack at night. When they are aware that their positions are known to us, they frequently fire tracer bullets and rifle grenades�this is searching fire intended to make us retaliate and reveal our positions.

At times hostile patrols penetrate to our rear—this generally occurs during the first half of the night.

(3) Action against Parachutists.—The following information from Japanese sources was included in an enemy order governing the defense of an airfield against U.S. parachutists:

Hostile parachute units, when attacking airfields while the wind is blowing, will fly in down-wind* bail out against the wind, and descend with the current. The parachutists, as a general rule, will descend after hostile forces have strafed or bombed our defenses.

In defense against such parachutist attacks, site machine-gun and rifle positions around and near the airfield so that these weapons can be fired up and against the wind.

Keeping in mind the rate of descent (16.4 feet per second) and the wind current, sights will be aligned at a point below and down-wind to the parachutists.

The following table gives some examples of how to sight your rifle or machine gun:

1,640 yds 8 leads down 3 leads right.

1,312 yds 6 leads down 2 leads right.

1,094 yds 3 leads down 2 leads right.

656 yds 3 leads down 1 lead right.

328 yds aim at feet.

¹ "How Japanese Raiders Demolish Artillery," a section based on enemy sources, appeared in Intelligence Bulletin, Vol. II, No. 4, pp. 13-16.
² Although the two attacks referred to above took place as planned, both were almost complete failures.