Chapter VII: Tactics of the Japanese Army

Part II: Application of Tactics

Section VI: Antiaircraft

1. GENERAL CLASSIFICATION OF JAPANESE ANTIAIRCRAFT MEASURES. a. Passive. Passive antiaircraft measures consist of concealment, camouflage, and dummy works. By these means, an attempt is made to hide the defended object from air observation, to make it look like either a natural part of the terrain or a non-military objective, or to construct dummy works so that they will draw the fire of attacking aircraft. Frequently combinations of these methods are used. On the whole, camouflage in the field and of small installations has been excellent, while attempts at camouflage of large installations so far covered have not been particularly successful. Manuals place considerable emphasis on the use of both large and small-scale smoke screens, but this has not so far been observed in practice.

b. Active. Active measures in general are as follows:

(1) Antiaircraft guns of calibers ranging from 7.7-mm to 127-mm are known to be in use. These are high velocity weapons with effective ranges up to altitudes of 25,000 feet. They are used for direct action against attacking planes, to shoot them down and to break up their bomb runs. Ammunition ranges from incendiary to high explosive fragmentation projectiles with time fuses.

(2) Barrage balloons are used for protection against dive bombers. These are usually camouflaged a greenish blue when defending objects on the water, and are difficult to see. They offer no protection against high level bombing, because their maximum elevation is not great enough—usually being about 1,000 feet.

(3) Night fighter planes, equipped with radar or operating in conjunction with ground searchlights, are used to seek out and destroy hostile planes.

2. ORGANIZATION. a. Areas to be defended. Areas to be defended are: (1) important points, such as bridges, beachheads or docks, anchorages, isolated military stores, and movement of troop columns thru defiles; (2) important towns or cities; (3) airfields. No definite priority can be placed on these areas, for it depends on their relative importance which is subject to change.

b. Home defense. For active defense, the Japanese homeland is divided into antiaircraft defense areas. The organization of defense measures is usually entrusted to the senior Army officer in the district who coordinates the efforts of military, naval, and civilian units. The Army units include the fortress artillery of fortified zones, individual units of field antiaircraft artillery, and army aircraft.

3. SEARCHLIGHTS, FIRE CONTROL INSTRUMENTS, AND WARNING METHODS. a. Searchlight tactics. (1) At the end of 1943, Japanese searchlight operation was still ragged and inefficient compared with Allied standards. However, they were rapidly improving their methods. There were indications that some type of radio direction finder for searchlights was coming into use by the Japanese in certain areas. Reports state that some Allied aircraft have been picked up as soon as the searchlights were turned on and illuminated for as long as three minutes, even when evasive action was taken.

(2) It is believed, however, that the majority of Japanese searchlights are directed by sound locators.

(3) Lights apparently are controlled centrally, as they are frequently illuminated simultaneously, searching in the same direction.

(4) Cooperation between searchlights and night fighters has improved. Searchlights have frequently been seen waving vertically or scissoring, especially when about to focus on a plane. Searchlights have been waved together vertically on one side or the other of hostile aircraft, presumably to give direction to a night fighter.

(5) Emplacements are generally circular and from 15 feet to 35 feet in diameter, with most being of the larger size. Searchlights are generally emplaced in an oval pattern with the defended area in the center.

b. Fire-control instruments. (1) Japanese fire control instruments examined to date show no new improvement, and in general, they are obsolete judged by modern standards. The standard heavy antiaircraft (75 mm.) guns recovered in the Aleutians, the Solomons, and New Guinea were all manually operated from data transmitted by voice to the gun crew members from the operators of off-carriage instruments. No directors have been used in conjunction with the 40 mm, 25 mm, or 20 mm automatic cannons. However, reports indicate that Allied flyers have experienced heavy accurate antiaircraft fire over Japanese bases, even through cloud cover, which would seem to indicate that fire-control equipment of more advanced design is in use.

(2) It is a common practice for single Japanese planes to fly at the same altitude as enemy bombers although well out of range. These planes make no effort at interception; their evident purpose is to transmit to the guns data as to the elevation and speed of the target, for when these "spotter" planes are present, the corrections of antiaircraft fire have been rapid.

c. Warning methods. Three warning methods are in general use by the Japanese:

(1) Sound locators of the trumpet type are still used, although they are not very effective against modern high speed planes.

(2) Radar is in use in many important defenses, but its range appears to be rather limited. Development by the Japanese in this field has lagged behind that of Allied nations. The number of occasions when Allied planes have reached their objective undetected would indicate that the use of radar is limited.

(3) Visual observers are extensively used to give warning. Outposts with the mission of reporting the movement of hostile planes are placed in advantageous positions. These outposts attempt to get as close as possible to points from which they can observe the movement of enemy planes from airfields. It must be expected that some of these groups will actually be within the enemy lines. Other observers are posted on high terrain features and on ships. They work in short tours of observation with frequent relief, and report plane movements by radio. Their equipment for observation is usually limited to binoculars. There are instances where the only warning system employed consisted of the gun crew itself, acting as observers.

4. POSITIONS. a. Location. (1) Japanese antiaircraft companies observed are usually situated within a 1-mile radius around the area to be defended, with the greatest concentration of guns between the defended areas and the sea approaches thereto, along shore lines, and in the direction of enemy territory. Guns are mounted both in single positions and in batteries of from 2 to 12 guns. The distance between guns in both heavy and medium companies varies from 40 to 250 feet, with the majority of revetments between 50 and 110 feet apart. Machine guns usually are placed either within the group or a short distance from the group for protection against low flying aircraft.

Figure 89. Four Gun Heavy Antiaircraft Battery (Emplacements Empty). Emplacements are built of earth over which grass has grown. Pattern is a shallow arc with fire control installations in center. A three-gun light antiaircraft and a two-gun light antiaircraft are also present. The large emplacements could house 75-mm or l05-mm guns. The small emplacements are probably for heavy machine gun or 13-mm antiaircraft.

Figure 89. Continued.

(2) The only distinction between the locations of medium and heavy antiaircraft companies is that medium companies are rarely placed outside the 1-mile radius except along beaches, while some heavy companies may be as far as 4 miles from the defended area.

b. Arrangement. In general the arrangement of the positions is dependent on the number of guns involved and the terrain. When 3 guns are used, the position is usually in the form of a triangle, with 1 gun at each corner and the command post in the center. In the case of 4 guns, the shape of the position is usually rectangular. If more than 4 guns are employed, the position is normally in the shape of a shallow arc. Small caliber, automatic guns are normally employed nearby for close in protection from low flying planes. Where the terrain permits, some gun positions may be located on commanding ground, thus providing for all around traverse. Command posts vary in both number and location relative to the gun positions. They are usually located inside and near the mid-point of the battery pattern.

Figures 90, 91. Note the Rough Trapezoidal Pattern of this Four-Gun Heavy 75-mm Antiaircraft Battery. The command post is centrally located. This pattern is used most often at permanent, strongly established Japanese bases. The emplacements are shallow excavations with thick, strong revetments.

Figure 91.

5. GUN EMPLACEMENTS. a. Standard type. The standard type of gun emplacement used almost exclusively is of circular or semi-circular construction, either level with the surface of the ground or slightly dug in. It is surrounded by a revetment built up of logs, coral, sand bags, and other materials to protect the gun and its crew. The opening usually is protected by a blast wall. A variation of this type of emplacement is constructed with two concentric circular revetments. (This type is commonly called the "doughnut.") The almost rigid adherence to these types of emplacements makes them readily identified from the air. Recently more care has been taken to conceal them by decreasing the slope of the revetment and planting it with natural growth so that shadows will not be so apparent.

b. Sizes. The caliber of the gun can be determined roughly from the size of the emplacement. Approximate sizes of emplacements for certain guns are listed below:

105-mm		Normally 20 feet in diameter.
75-mm mobile		Normally 20 feet in diameter.
75-mm static		Normally 15 feet in diameter.
Machine cannon		Normally 13-15 feet in diameter.
13-mm machine guns		Normally 8 feet in diameter.

c. Camouflage. Little or no effort is made to camouflage or conceal the guns, but extensive use is made of dummy and alternate positions, even to the extent of constructing dummy guns.

6. EMPLOYMENT OF ANTIAIRCRAFT. a. General. It is normal to attach antiaircraft units to divisions. Their missions are the same as those assigned in Allied armies, but the division commander is given direct control over them.

b. All antiaircraft guns are dual purpose, most being capable of a minus depression; however, there is no evidence of armor-piercing ammunition for the larger caliber guns.

Figure 92.

Figure 93. Sketch of 75-mm antiaircraft gun in earth revetment. Note partially excavated type of emplacement with high revetment and built-in Ready Magazine. Note also zigzag entrance trench.

c. Methods of fire. (1) All guns in a position frequently concentrate their fire on the leading plane of a formation and fire on succeeding planes if time permits.

(2) Colored spotting rounds often are used.

Figure 94. Six-Gun Heavy (105-mm) Antiaircraft Battery. Note shallow arc pattern with command post in center.

Figure 94. Continued.

(3) Instances of accurate fire above the overcast indicate the probability of radio direction equipment.

(4) In areas where the ground is often blanketed with clouds, such as in the Aleutians, all guns direct their fire at the opening in the clouds where the enemy planes may normally be expected to appear.

(5) Barrage fire has been employed.

(6) In jungle country, the Japanese have shown an increased tendency to attack with light machine gun and rifle-fire against low flying aircraft. Such fire is encountered particularly along lines of communication, and its effectiveness should not be discounted.

Figure 95. New Type Double Revetment (Nusa Island battery across Wavieng channel), showing detail of construction.

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