Some Japanese Defensive Methods, WWII Tactical and Technical Trends, No. 24, May 6, 1943 (Lone Sentry)

In previous issues of Tactical and Technical Trends, references have been made to some defensive tactics used by the Japanese. The following notes from British sources give added emphasis to this subject and are reported here in order to facilitate recognition of these tactics.

a. General

Japanese tactical methods in the defense conform basically to normal practice, but they are characterized by a very high standard of camouflage. Except in marshy country, where the Japanese build up to as much as 8 feet above ground level, it is difficult to spot their positions, which are skillfully hidden under bushes, hedges, and buildings and even under the roots of big trees. Whether in jungle or other country, the principle of all-around defense is strictly applied, and positions have so far presented no weak spots. Defended areas, however small, are self-contained with regard to ammunition and food, and they are stubbornly defended--literally to the last man. Japanese seriously wounded have been found still grasping hand grenades which they have been too weak to throw, and on other occasions repeated offers of quarter in a hopeless situation have been refused.

The information given below is based on experiences in New Guinea and the Solomons, and while principles--such as depth in the defense, all-around defense, and the application of camouflage--do not alter, details such as the employment of supporting weapons and the construction of defenses, will vary considerably according to the nature of the country. This point should be remembered when studying what the Japanese have done in the dense jungle of New Guinea, so as to be prepared for something different in the more open spaces of, say, Central Burma and China.

b. Organization of Defensive Position

The Japanese choose positions on commanding ground and site their defended areas in great depth along the line of communication.

Weapons are sited to cover all approaches and are protected by booby traps. Weapon pits are small and cleverly concealed. They normally contain one or two men and are often linked by tunnels. Whether in swampy or dry ground, overhead cover is often constructed.

Automatic weapons are sited to fire along prepared lines which intersect. These lines are cut in the jungle to a height of about 2 feet, presenting a tunnel effect. 30-caliber heavy MGs are likely to be sited well forward and sub-allotted to platoon localities. Positions containing automatic weapons are frequently protected by snipers in trees near the position. Men in trees have also been reported on the flanks of positions.

In swampy areas, two types of earthworks are constructed. The first, called in the Southwest Pacific the "bunker" type, consists of a trench with closely timbered sides and top. The trench is covered by a mound which is built up with coconut-log piles laid lengthwise and packed with earth. The height of the mound and the depth of the trench vary according to the level of the swamp water. Some mounds rise to about 8 feet above ground level. These mounds have slits at ground level for automatic weapons, and the positions are connected by crawl trenches. The mounds give protection to the defenders against mortar and antipersonnel bombs and limit the effect of 25-pounder (88-mm) shells. Positions are camouflaged with local natural materials.

The second type of earthwork is similar in appearance to the first, but it is constructed without loopholes and used for concealment and protection from artillery and mortar fire. Attacking troops, attracted by these raised earthworks, tend to make them their objectives and are then caught in the fire from posts constructed at ground level on the flanks and in rear of these earthworks.

In addition to the construction of these earthworks, the Japanese pay particular attention to the careful digging of dugouts. In the Solomon Islands, for instance, it was found that hand grenades could be thrown into Japanese dugouts but, owing to the special construction of the entrance, they exploded harmlessly inside without killing the occupants, who were subsequently able to emerge and fire into the rear of our troops. In this area the dugouts were cut back into a hillside and were sited so as to be mutually supporting. They were constructed to hold about eight men each and were faced on the front and flanks with sand bags and steel plates. Their layout was as shown in the diagram (see Tactical and Technical Trends, No. 10, p. 13).

Telephone cables are laid between defended localities, but according to information received so far, visual methods of intercommunication, such as flag or shutter, have not been employed.

c. Conduct of Defense

In jungle country the fire fight takes place at ranges of between 50 and 100 yards. It has been found especially necessary to make a short pause between igniting the fuze of a grenade and throwing it, as otherwise the Japanese are adept at throwing them back.

The Japanese make frequent use of small local counterattacks conducted by 8 or 10 men and led by an officer.

d. Deceptive Tactics; New Guinea

The following notes summarize some of the tactics used by the Japanese in the New Guinea area. The extensive use again made of deceptive tactics should be noted.

(1) When the Japanese met the enemy line of skirmishers they fired all their machine guns into the tree-tops above their opponents. As soon as this fire was countered by Allied machine guns, the Japanese mortars opened up on these machine-gun positions.

(2) On several occasions when the Allied line of skirmishers was met, large numbers of Japanese ran forward and were met by a withering machine-gun fire. They immediately turned round and fled. Allied troops with the usual cry of "After the bastards" immediately rushed forward with fixed bayonets. Immediately, the fleeing Japanese threw themselves on the ground and Allied soldiers ran into machine-gun fire from the Japanese rear.

(3) In the Milne Bay area the Japanese plan was to advance and attack during the night and then to withdraw during the daytime, leaving dozens of their men in the tops of coconut palms, and in the jungle, with automatic weapons. As Allied forces advanced the next day, they were harassed by these remnants. Often the Japanese were tied in the tops of the palm trees and remained there after they were shot.

(4) There were times when it was felt that the Japanese troops might have surrendered, but in no case did they do so. It was a question of keeping at them until every man was killed.

(5) Counter Tactics

The plan eventually developed by Allied forces, as they advanced during the day, was to drop a platoon or two each 4 to 5 hundred yards apart as they advanced, and eventually they would meet the main Japanese forces. By nightfall each of the independent posts and the main force would slash a perimeter clearing of about 200 yards diameter around their posts, rig trip wires at the edge, and then confidently await the Japanese night attack. This appeared to upset the Japanese plan and proved very successful.