Technical Manual, U.S. War Department, October 1, 1944
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Chapter VII: Tactics of the Japanese Army
Part I: General Tactical Doctrine
Section III: Defensive
1. GENERAL. a. Japanese attitude. The defensive form of combat generally has been distasteful to the Japanese, and they have been very reluctant to admit that the Imperial Army would ever be forced to engage in this form of combat. So pronounced has been their dislike for the defensive that tactical problems illustrating this type of combat are extremely rare.
b. Object. The object of the defensive is to inflict on the superior hostile forces such losses by fire power, disposed appropriately on the terrain and behind man-made defensive works, that the initial disparity of forces becomes equalized to the point of authorizing a passage eventually to the offensive.
c. Doctrine. The old Combat Regulations (Sento Koyo), superseded in November, 1938, based discussion of the defensive on the active defense. The newer regulation (Sakusen Yomurei) takes the passive defense, assumed in the presence of overwhelmingly superior forces, as the typical case, of which the active defense is a variant calling for special discussion. This latter viewpoint is definitely contrary to former practice where a return to the offensive is always present in the plans for the defense, even though the initial dispositions are not those of an active defense in the true tactical sense of the word. This indicates a change in official emphasis, but probably means no real change in the practice of the defense, since in actual combat and in illustrative problems there is always present the characteristics of active defense.
2. DEFENSE OF A POSITION. a. Selection of the position. The qualities sought for the main battle position (observation, protected flanks, fields of fire, covered lines of communications, obstacles, etc.) are those standard in all schools of military doctrine. In accordance with the current trend, the Japanese emphasize the importance of antitank obstacles across the front and flanks of their position. In the presence of an enemy who may use gas, the main line of resistance will avoid depressions where it is likely to accumulate. The importance of cover and concealment is fully recognized. Reconnaissance for the position is made by the division commander, assisted by his artillery and engineer commanders as well as other appropriate staff officers.
b. Occupation of the position. (1) When the general outline of the position has been determined, the division commander directs the subordinate elements of his command to their respective defense areas where they deploy directly upon the position which they are to occupy. The division commander directs his cavalry (often reinforced by some infantry) to cover the deployment and organization of the position. This force takes position far enough in advance of the area to be organized to keep hostile artillery fire off the main line of resistance. The division commander's reconnaissance must include:
(a) Determination of the probable direction of hostile attack.
(b) The probable direction of a division counterattack or counteroffensive.
(c) Antitank measures.
(d) The assignment of troops within the defensive area.
(e) The use of artillery including antiaircraft.
(f) The composition and location of the division reserve.
(g) The use of tanks.
(h) Communications and liaison.
The completeness of the reconnaissance is dependent on the time available. He then issues his defense order.
c. Organization of the position. (1) The defense is based on a main position (shujinchitai) which is held to the last extremity. The division commander normally divides the defensive position into right and left sectors (chiku) the defense of which he assigns to his two senior infantry commanders. In cases where the front is unusually broad, or a counter-offensive is planned, he may add a center sector. The Infantry is disposed along the main line of resistance by units of battalions, with frontages determined by the terrain and mission. When a broad defense is adopted, battalion centers of resistance are organized for an all-round, independent defense, in which the lateral intervals can only be partially covered by fire. In this form of defense, reserve units, kept as large as possible, are held mobile to attack hostile elements which filter through. Battalion frontages in the broad defense along the main line of resistance may approach 3,000 yards, while the normal defense frontages average from 800 to 2,000 yards.
(2) Support and local reserve units are deployed behind the front line infantry to give the position a depth of 700 to 1,500 yards. Throughout this zone automatic and antitank weapons are echeloned in depth. Usually heavy machine guns are found deployed along the support position, from which they attempt to cover the front with interlocking fires (criss-cross fires).
3. THE OUTPOST POSITION. a. The outpost position (Keikai Jinchi) is indicated by the division defense order and is garrisoned by troops dispatched by the sector commanders. The order may specify the strength of the garrison, its mission, and manner of withdrawal. Troops on the outpost line of resistance normally pass to division reserve when relieved. The outpost line of resistance is generally from 1,500 to 3,000 yards in front of the main line of resistance, so as to be within supporting range of light artillery. Combat Regulations tend to recommend the shorter distance so as to obtain the fire support of machine guns from the main line of resistance. However, in observed practice, the Japanese seem to attach little importance to the uncertain support of long-range machine gun fire.
b. The normal missions of the outpost line of resistance are (1) to obtain enemy information by observation and patrolling, (2) to cover the main line of resistance and prevent its surprise, (3) to delay the hostile attack on the main line of resistance, and (4) to act as an advance defensive position (Zenshin Jinchi). Missions (1) and (2) are the minimum case, where the outpost line of resistance is not much more than a line for observation and reconnaissance with little defense strength. Missions (3) and (4), frequently present in observed practice, imply a considerable increase in defensive means approaching that of a true advanced defensive position.
c. The troops assigned to garrison the outpost line of resistance, while variable in strength with the mission assigned, are kept to a minimum. For the front of a division, 1 to 2 battalions of infantry were normal in the problems consulted. Comments on these problems indicate that about 2,000 yards for the infantry company is considered the absolute maximum extension consonant with the retention of any sort of control by the unit commander. With the usual weak allotment of troops, it is impossible to hold the line continuously. Instead, important points are occupied in some strength, while the intervals are covered by observation and fire as far as possible. The Japanese do not expect to be able to organize a continuous system of infantry and artillery fires in front of the outpost line of resistance. With the help of attached engineers, the infantry strengthens the outpost position by defensive works to the extent permitted in the time available. In the case of the defense on a very wide front the outpost line of resistance is reduced to a line of observers, or may even be dispensed with entirely.
4. ADVANCED DEFENSIVE POSITION. a. The division commander at times may order the occupation and organization of an advanced defensive position (Zenshin Jinchi) in the zone between the outpost line of resistance and the main battle position. The purpose of such a position is to prevent as long as possible the occupation of critical points of terrain by hostile forces near the main defensive zone, to delay the enemy preparations for the attack, and to induce the enemy to launch his attack in a false direction which will expose his flank. The organization of a formal advance defensive position is not standard Japanese practice, although the assignment of such a mission to the outpost position is not uncommon. Typical cases where the advanced positions have been organized are: (1) where in order to obtain observation the outpost line of resistance has been pushed well forward, leaving an important ridge in the foreground of the main battle position ungarrisoned; and (2) where an oblique position is organized between the outpost position and the main battle position, with one flank resting on the outpost line of resistance while the other rests on the main line of resistance, thus inducing the enemy to expose a flank.
b. The garrison of the advance position may come from the troops assigned to the outpost position or from those of the main battle position, reinforced by machine guns and antitank weapons. Artillery elements may be assigned support missions. The delicacy of withdrawing this force is fully appreciated by the Japanese, and the division commander is cautioned to issue clear and simple missions to this force and to specify the time and manner of withdrawal.
c. In cases where the division commander elects not to organize an advance position, the zone between the outpost position and the main battle position is covered by observers sent forward by the front line infantry battalions. These troops patrol the foreground, cooperate with those of the outpost line of resistance, and execute local reconnaissance.
5. RESERVES. a. Reserves are held out by all units from the company upward for the purpose of executing counterattacks. The division reserve generally varies in size from 1 to 3 battalions. Its position is initially from 5,500 to 6,500 yards in rear of the main line of resistance, in a sheltered position conveniently situated with respect to the probable counterattack of the division. Tanks often will be attached to this force.
Motor transportation generally is not attached to the reserve because of the paucity of organic motor transport in the division.
b. When the division commander has planned an active defense, the general reserve as a rule will not exceed a third of the infantry strength, since front line units themselves are expected to return to the offensive at the earliest opportunity.
6. ARTILLERY. The artillery is disposed in depth behind the main line of resistance so as to be able to mass its fire in support of the main position in the area of the hostile probable main effort. One or two artillery companies may be initially in forward positions to support the outpost positions or an advanced defensive position. Artillery positions generally are echeloned through a zone about 2,500 yards in depth, extending to the rear from a line about 1,700 to 2,200 yards behind the main line of resistance. Ground observation is not considered effective under normal conditions for ranges over 5,500 yards.
7. COMMAND POSTS. a. General. Command posts generally are established in well sheltered positions in rear of the main line of resistance; that of the division is usually located at a distance of about 5,500 yards, that of the infantry group at about 2,700 yards, and that of the infantry regiment at about 1,300 yards in rear of the main line of resistance.
b. Organization of the ground. (1) In the early phases of the reconnaissance of the position, the division commander gives initial instructions to his engineer regarding the supplying of entrenching tools, material, and equipment. The defense order indicates the priority of work, a typical one being the following:
(a) Principal points on the main line of resistance.
(b) Fields of fire and observation posts of the main line of resistance.
(c) Obstacles in front of the main line of resistance.
(d) Communications, trenches, and personnel shelters.
(2) In tactical problems it is seldom assumed that there is time available for elaborate field works. The division usually has from about 3 hours to a half day to complete its organization of the ground. Three hours is considered the minimum required to organize a rudimentary system of trenches and obstacles along the main line of resistance. The time-work unit in engineering calculations is the 12-man squad which is considered capable of digging about 25 yards of standing fire trench in a little over 3 hours. In situations in which the use of gas by the enemy is expected, the division commander will order the distribution of protective materials at suitable points throughout the area. Stress is laid on camouflage and the construction of dummy field works, the completeness of which is dependent upon the time available. A typical plan followed by the Japanese in the construction of the field works of a company position on the main line of resistance is illustrated in figures 86, 87, and 88.
c. Conduct of the defense. (a) Advanced elements. As the enemy approaches the position, he will encounter first the advanced elements of the defense (the outpost line of resistance or advanced defensive position). These forward elements conduct themselves in accordance with their mission which normally directs their withdrawal into division reserve before becoming seriously engaged. Artillery companies in forward positions delay the hostile advance, cover the withdrawal of the infantry, and then fall back to prepared positions in the artillery zone where they revert to the control of their organic commander. The cavalry which has withdrawn to the flank, while maintaining contact with the advance positions, will carry out its normal missions.
(b) Defense of the main line of resistance. As the hostile infantry forms up for the attack on the main line of resistance, the defensive artillery brings down its counter preparation fires. Tanks may be sent forward, covered by artillery, to upset the preparations of the enemy. As the hostile attack enters the zone of infantry fires, the sector commanders conduct the defense of their sectors, first by fire, then by the bayonet in front of their entrenchments. Commanders of all units counterattack unhesitatingly as the integrity of their positions becomes threatened by the hostile attack. The artillery assists the close-in defense by standing barrages and concentrations brought down within the defensive position.
(c) The counterattack or counteroffensive. The division commander is constantly on the alert to determine the proper time for the division counterattack or counteroffensive. The favorable moment will generally be at the time the hostile attack has been stalled; when the enemy has blundered into an unfavorable position; when a favorable opportunity has been created by a successful local counterattack; and when the enemy pauses to reorganize or consolidate his position. The plan for a return to the offensive will be made tentatively well in advance of the occurrence of the opportunity. The direction of the counterattack generally will be aimed at an envelopment; however, at times, the situation may compel a purely frontal attack. The mass of artillery, and tanks if present, will support the counterattack or counteroffensive. The division commander may directly control the counteroffensive, or he may delegate control to a sector commander.
8. COMMENTS. a. Aggressive character. Since the defensive in Japanese regulations and military writings is branded as a negative form of combat, un-Japanese in essence and spirit, it has been very difficult to write a tactical problem for which officers were willing to advocate a defensive solution. In problems studied, the basic decision to defend already had been made by the division commander, a school device to control the offensive elan of the student officers. Even when thus forced on the defensive. Japanese officers have the return to the offensive always uppermost in their minds and are quick to launch counterattacks, large and small, coordinated and uncoordinated, on the slightest provocation. On the maneuver ground, troops are always ready to abandon their prearranged system of infantry fires to meet the attacker with the bayonet in front of their trenches. The defects of a defense so conducted are glaring to the occidental student of tactics, but its positive and aggressive character has virtues which will, on occasions, upset a careless or overconfident attacker.
b. Other characteristics. In spite of the usual instructions issued relative to the need of echelonment in depth of the defense, there is an apparent tendency to concentrate a disproportionate strength in the front lines. This is especially true of the special weapons (machine guns, battalion guns, etc.). The appearance of the "broad defense" in Combat Regulations appears to be a recognition of the increased strength of frontal resistance of modern infantry, as well as an official corrective to the often remarked Japanese tendency to a shoulder-to-shoulder disposition of units both on the attack and defense.
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