A report on WWII Japanese defensive tactics, from Tactical and Technical Trends, No. 31, August 12, 1943. [DISCLAIMER: The following text is taken from the U.S. War Department publication Tactical and Technical Trends. As with all wartime intelligence information, data may be incomplete or inaccurate. No attempt has been made to update or correct the text. Any views or opinions expressed do not necessarily represent those of the website.]

JAPANESE CONDUCT OF THE DEFENSE 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 supporting. 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.

Back to Articles by Subject | Intel Bulletin by Issue | T&TT by Issue | Home Page