Japanese Antiaircraft Fire, WWII Tactical and Technical Trends, No. 42, January 13, 1944 (Lone Sentry)

Antiaircraft weapons have, to a considerable extent, kept pace with the innovations and developments in aerial warfare in all theaters. Comment on some interesting phases of Japanese antiaircraft operations, based on experiences of Allied airmen, are contained in the following review of this question which appeared in the December 1943 issue (Bulletin 18) of AFGIB (Air Forces General Information Bulletin).

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Over-all performance of the Japanese antiaircraft artillery defense system is definitely inferior to that of the other major contestants in this war.

Apparently lacking electrically-operated data computers, Japanese ground batteries direct their AA fire by the same off carriage methods which the United States found ineffective during World War I and subsequently abandoned. (For reference to Japanese height finder, see Tactical and Technical Trends, No. 39, p. 30). They are chronically inaccurate during the early part of an engagement, and as a result, the number of our aircraft destroyed or damaged by Jap antiaircraft fire has been very small.

It is difficult to make many authentic generalities about the Japanese AA system, which extends thousands of miles from the Solomons to Shimushu, because the defenses differ sharply from target to target. As the nature and importance of the targets vary, so do the accuracy and intensity of the antiaircraft fire with which the Japanese defend them.

Germany has been able to mobilize hundreds of heavy batteries, manned by skilled crews, to protect the vital targets within range of our bombers. But the Japanese, perhaps because of a shortage of materiel and expertly trained gun crews, have had to concentrate their best defenses around relatively few important and oft-bombed objectives, leaving other targets defended meagerly or not at all.

Antiaircraft fire from naval units, particularly battleships, cruisers and aircraft carriers, has generally proved more effective than the fire from land-based batteries. In the South Pacific and Southwest Pacific, where our air power has tangled frequently with Jap sea power, airmen have reported that the naval three- and five-inch guns can put up an intense and accurate barrage to protect a task force.

However, even the best defenses over the most vital targets on land or afloat, have not compared in results to German flak (for reference to German flak, see Tactical and Technical Trends, No. 35, p. 3).

During the 14 months of our operations against Kiska, our losses to antiaircraft fire were a very small percentage of the sorties flown. Similarly unimpressive has been the over-all performance in other theaters, although the defenses of certain key targets are good enough to be dangerous.

Some general conclusions have been reached about the layout and disposition of Japanese AA batteries.

Heavy and medium batteries are usually situated within a mile radius of the target, although the heavy batteries may sometimes be found up to four miles from the defended area. The medium batteries are almost invariably within the mile radius since they are designed primarily for protection against a diving or gliding aircraft.

Most of the guns and automatic weapons are usually concentrated between the defended area and enemy territory, in the direction of the sea approaches, and along the shoreline.

They are normally laid out in one of four patterns: a line, an arc, a quadrangle or a triangle. The linear pattern may include from two to 12 guns, and the arcuate, from three to 10, frequently reinforced with a few scattered light antiaircraft gun positions. The triangular and quadrilateral patterns have three and four guns respectively.

An independent AA battalion may contain three batteries of six guns each. Normally, these are 75-mm guns, the Japs' main heavy weapon, but may include one battery of 105- or 155-mm guns. Planes flying over Kahili have seen a few AA bursts between 30,000 and 36,000 feet, and a formation of B-17s flying over Rabaul reported AA fire bursting at 32,000 feet and above, indicating the occasional use of weapons heavier than the 75-mm. Four 120-mm dual purpose naval guns were also found on Kiska after the occupation of that island. Of the 69 AA weapons on the island, however, 22 were 75-mm.

The 75-mm gun, model 1928, an improvement over a similar weapon, model 1922, has a maximum vertical range of slightly more than 32,000 feet. But actually the gun's effective ceiling is much lower, about 26,000 feet. Its practical rate of fire is 15 rounds per minute.

An AA defense regiment will include two battalions of heavy AA; an automatic weapon unit having 18 or more weapons each, usually 20-mm machine cannon;* one battalion of 12 or more searchlights and 12 or more sound locators, usually one 7.7-mm or 13.2-mm machine gun for every two AA guns.

One of the newest Japanese naval AA weapons is the 25-mm pompom which may have either two or three barrels. Ten of the twin-barreled models were part of the defenses of Kiska. The effective ceiling of these weapons is about 3,000 feet. The 20-mm type weapon, which can be used either as antiaircraft or antitank, fires 120 rounds a minute and is most effective under 7,000 feet.

The two light machine guns, the 7.7-mm and 13-mm, corresponding approximately to the U.S. .30 caliber and .50 caliber machine guns, are most effective under 3,500 feet.

The Japanese follow the fundamental rule of never divulging their position by gunfire. They will often withhold their AA fire until they are absolutely positive they have been discovered, and then begin firing with every weapon available, including their rifles. Often they set up a barrage of trench-mortar fire against our minimum altitude attacks.

The Japanese have been experimenting with new types of AA projectiles, such as incendiary bombs propelled from the ground by rockets. The Tenth Air Force has reported the use of parachute canisters propelled from a mortar. These canisters were encountered at about 1,000 feet, suspended from their paper parachutes, apparently designed to explode when the parachute cord was jerked by contact with the airplane.

The crews of a formation of B-24s which attacked Vunakanau airdrome at Rabaul on 12 June saw the following new AA phenomenon: "A large white ball ascended to about 7,000 feet and exploded into myriad small red fragments bursting out in every direction. Some of these went to about 7,500 feet."

However, such strange and uncommon occurrences have proved interesting so far only because they indicate that the Japanese are experimenting with new AA artillery devices, doubtless because they have experienced difficulties with their standard weapons.

Japanese ground batteries of heavy guns apparently have no electrically-operated data computers, and the guns are aimed by fixed sights. Lateral and vertical deflection, slant range and super-elevation are determined by using drums, dials and disks located on the gun.

It is natural, therefore, that the Germans, with their modern electrical data computing equipment, achieve greater accuracy than the Japanese.

The Japs have achieved their greatest accuracy at medium altitudes, the accuracy falling off sharply above 15,000 feet.

Sometimes the Japanese use stalking planes, flying at the same altitude as our bombers, to relay information to the gun crews. When these stalkers are present, adjustment of antiaircraft fire has been more rapid than normally. The Japanese are also clever about pre-estimating the altitude of clouds as a factor in determining the altitude of the attacking planes.

Although Japanese AA fire is usually inaccurate when only one bombing approach is made, a second approach at the same altitude and from the same direction will very often encounter accurate AA fire, since the gunners can then use data computed from the first approach.

The Japanese have even been known to use data computed one day for firing the next day. In one particular instance in the China theater, when the same target was attacked on two successive days, a very heavy barrage of antiaircraft fire was laid down on the second day at the approximate altitude at which the attack had been made on the previous day.

The accuracy of the Japs' light AA fire varies with the experience and skill of the individual gunners. However, it is generally fairly accurate under 3,500 feet.

The target area will probably be protected by machine guns from any angle of approach. Hence, the best chance of success for a low level attack will result from surprising the gunners by approaching so as to utilize cover of hills and trees.

Our night missions against Japanese objectives have encountered some searchlight activity, but the synchronization between searchlights and AA artillery is usually poor or lacking entirely. However, an exception to this general rule was reported from the Southwest Pacific following a mission on 13 June against the Vunakanau airfield at Rabaul. A mission report gave the following description of the searchlight activity:

"Some aircraft, by gliding or evasive approaches while antiaircraft guns and searchlights were occupied elsewhere, did their bombing and encountered little or no antiaircraft fire. Those singled out reported that antiaircraft fire, heavy and light, was coming from all areas and was accurate.....

"There were very many searchlights in operation, as usual. They were synchronized with light caliber antiaircraft weapons. Even searchlights from the Lakunai and town area assisted over Vunakanau. Apparent signalling was strongly evident, as many searchlights were noted waving vertically or scissoring, especially when able to focus on an aircraft. A new procedure noticed was for a pair of searchlights to wave together vertically, one on either side of our aircraft, presumably to give direction to a night fighter. Four batteries in a diamond-shaped pattern around Vunakanau synchronized, forming a cone."

Since Rabaul is the key Japanese base in the Southwest Pacific and has been attacked repeatedly, it is not surprising that the Japs have concentrated some of their strongest and best defenses around this base.

This is the policy the Japanese have followed in Burma where a handful of the most important targets are strongly protected at the expense of the defenses of other targets.

A detailed study of Jap AA fire in this theater for four months in 1943 -- 1 April to 31 July -- has revealed some interesting facts about the Japanese employment of antiaircraft artillery.

During this period, AA batteries were stripped from some targets to boost the defenses of a few crucial objectives which our forces were attacking frequently.

Most of the hits on our aircraft were scored over such targets as the Myitnge Bridge, Mahlwagon railroad yards, Maymyo, Mandalay and the Chauk oil fields, all important supply and communication centers which the Tenth Air Force was bombing consistently.

The concentration of AA defense around these centers was apparently achieved by reducing the defenses at Rangoon and other cities in Burma. Our missions against Rangoon met both heavy and light antiaircraft fire but the accuracy had fallen off compared to previous months.

With the exception of these few points, where the Japanese had focused their most efficient batteries, AA fire in Burma was not a serious threat to our offensive activities.

The Japs had their best record in July when our fighters, grounded for the most part during June by the monsoons, resumed their bombing and strafing of Japanese installations and troop camps in northern Burma. Large concentrations of automatic weapons and small arms fire were noted from Sumprabum and Kamaing in this area.

Another reason for the increase in accuracy was the heavy monsoon overcast which forced our aircraft to bomb from lower altitudes that are more favorable to Japanese AA equipment. Our aircraft were compelled to fly under the overcast in many cases, and the Japanese had evidently pre-determined the altitude of this overcast, thus having one element of their firing data already placed on their fire control instruments.

The conclusion of this study was that Japanese AA weapons and personnel have great difficulty in coping with targets flying at our service speeds and altitudes.

*In some cases 37-mm or 40-mm guns may be encountered. Sometimes 25-mm pompoms are found, but these are naval weapons.