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"Type 98 AA/AT Gun (Japan)" from Intelligence Bulletin

[Intelligence Bulletin Cover]   A report on the Japanese Type 98 20-mm AA/AT Gun, from the Intelligence Bulletin, September 1943.

[Editor's Note: The following article is wartime information on enemy tactics and equipment published for Allied soldiers. In most cases, more accurate data is available in postwar publications.]

TYPE 98 AA/AT GUN (Japan)


The Japanese Type 98 antiaircraft-antitank gun, 20-mm, is considered one of the enemy's best constructed and most efficient weapons. Most of its features were copied from a 20-mm rapid-fire gun manufactured by the Oerlikon Company, of Switzerland. In fact, some of the bearings in the carriage of a Type 98 recently examined by U.S. Ordnance experts bore a Swiss stamp. The Japanese weapon, weighing approximately 840 pounds, is relatively light and very maneuverable.


Weight   840 lbs
Elevation-9° to +81.9°
Traverse (pintle type)360°
Maximum horizontal range  5,450 yds
Maximum vertical range12,000 ft
Rate of fire120 rds per min
Muzzle velocity2,720 fs
Length of barrel70 calibers


a. Tube

A stamp on the tube of the weapon examined indicated it was made in December 1940.

The length of the tube is 57 1/6 inches with the muzzle brake, and 55 1/8 inches without it.

The locking of the tube to the receiver is accomplished by means of an interrupted thread bushing, which screws one-sixth of a turn into the receiver; this bushing is locked into position by a latch liner which fits into adjusting notches.

The muzzle brake is a large, fiat ring, which extends out about 1 inch from the muzzle. The tube extension has holes (see fig. 1) to allow room for gases to expand. These gases leave the muzzle under very high pressure, and exert a force against the flat ring. This aids the recoil action, disperses the muzzle blast, and breaks up the flash.

[Figure 1. - Japanese Model 98 AA/AT Gun (20 mm).]
Figure 1.—Japanese Model 98 AA/AT Gun (20 mm).

b. Magazine

The magazine is of the vertical box type, and has a capacity of 20 rounds. It fits into a slot in the top of the receiver, and is held in place by a shoulder and spring catch.

c. Carriage

The carriage weighs 685 pounds, and, in its traveling position, has an over-all length of 9 feet. Its body has a road-clearance of 1 foot. The trails are the split type, and a detachable third leg (outrigger) is provided. The trails have fixed spades, with holes so that stakes can be used in stabilizing the gun.

The carriage has no shield. Its wheels are made of wood with iron or steel tires. The wheels, equipped with lug rings, can be detached easily.

d. Recoil System

This consists of two spring-loaded cylinders, which have valves in their forward ends. These valves allow air to be drawn in during recoil, and, since the air cannot escape readily, it acts as a cushion in easing the counterrecoil. The length of the recoil is estimated to be 2 to 2 1/2 inches. It can be adjusted to a certain extent, but, once set, it becomes constant.

e. Sights

To date, no sights for this gun have been recovered. However, a report on the sight mount states that it has a small V-type open sight, with the head varying from about 2 to 8 inches from the notch. The mount has a mounting bracket for a sight of some type, and it is obvious from the accuracy obtained by the gun in combat that it is equipped with some type of modern telescopic sight. The small V-type open sight is probably used for initial aligning, or for short-range firing. It would be very ineffective as an open sight against aircraft.

The sight mount is rigidly fastened to the top of the carriage and to the sleigh by means of dovetailed, spring-locked mounting plates. The mount provides for setting in corrections, leads, deflections, and so forth, but how these devices operate cannot be thoroughly understood unless the actual sights are studied.


a. Getting into Position

It is estimated that an experienced gun crew could change the piece from a traveling position to a position for antiaircraft firing within a period of 3 minutes.

If necessary, this gun could be fired from its wheels as a split-trail artillery piece. In this case it could be placed in firing position from its traveling position within a few seconds. Under such conditions, the fire probably would not be very accurate. The weapon apparently is not designed for firing from the wheels, because it could not be cross-leveled, has no equalizer, and would be quite unstable.

The gun is placed into regular firing position from the traveling position by the following steps:

(1) The outrigger is attached to the front of the housing. This can be done rapidly because of the spring-loaded locking features.

(2) The axle is rotated to the rear, raising the wheels off the ground.

(3) The wheels are removed by releasing-spring catches on the axles. Removal of the wheels permits a 360-degree traverse at all elevations.

(4) The gun is cross-leveled by means of jacks on the outrigger and trails. The cross-levels are located on the upper carriage housing. The level vials are set in metal cylinders, which rotate one-half a turn and protect the vials when they are not in use.

b. Firing

In loading, the breech block strips individual cartridges from the magazine as the block moves forward and carries the shell into the firing chamber. As the shell is sealed into the chamber, its base is forced onto the extractor. (The extractor, spring-operated, is located at the bottom of the face of the breech block, and fits into a groove in the rear of the chamber.)

The gun may be fired either automatically or single shots, depending on the position of a change lever, which is located at the bottom of the rear the sleigh.

When the ammunition magazine is emptied, the bolt is held open by means of a spring-operated lever.

The gun has two safety features. The spring-charged lock on the firing handle must be pressed before the handle can be moved forward in preparation for firing. Also, the piece can be rendered "safe" merely by rotating the firing handle in a clockwise direction.

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