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"Japanese AA/AT 20-mm Machine Cannon" from Tactical and Technical Trends

The following intelligence report on the Japanese 20-mm antiaircraft and antitank gun was originally published in Tactical and Technical Trends, No. 38, November 18, 1943.

[DISCLAIMER: The following text is taken from the U.S. War Department publication Tactical and Technical Trends. As with all wartime intelligence information, data may be incomplete or inaccurate. No attempt has been made to update or correct the text. Any views or opinions expressed do not necessarily represent those of the website.]


The Japanese Model 98 (1938) 20-mm AA/AT machine cannon is a weapon of unusual appearance, but with many practical advantages. The following account of the gun has been taken from Special Series No. 18, "Japanese Infantry Weapons," which is in process of preparation by the Military Intelligence Division.

a. General

It is an all-purpose weapon. Because of its lightness in weight and maneuverability, it is an excellent gun for defense against low-flying bombers as well as against ground-strafing fighters. An experienced gun crew can probably place the piece in battery, ready for antiaircraft fire, in less than 3 minutes. In an emergency, the weapon could be fired as a straight artillery piece, because of its split trail and wooden wheels (see sketch).

[Japanese 20-mm AA/AT Machine Cannon]

b. Identification

The Model 98 20-mm AA/AT machine cannon may be identified by its general appearance. It is different from any other Japanese field piece, the front outrigger, the barrel traveling-lock and the marking which is on the top of the receiver are distinctive features.

[Kyuhachi Shiki - 98 Model]

(This marking, which is read "Kyuhachi Shiki" from top to bottom, means "98 Model.")

c. Characteristics

(1) General. It is automatic and gas-operated. The cycle of operation is loading, locking, firing, unlocking, extracting and ejecting; unlocking, extracting, and ejecting are done during recoil; loading, locking, and firing in counter-recoil.

The recoil mechanism consists of two spring-loaded cylinders that lie one on each side of the barrel. Air valves, located in the forward ends of the cylinders, allow air to be drawn into the cylinders during recoil; as the air cannot readily escape, it acts as a cushion during counter-recoil.

There is a vertical box-type magazine--with a capacity of 20 rounds--which fits into a slot in the top of the receiver and is held in place by a spring catch.

For traveling, towing shafts are inserted in slots at the end of the trails, and a traveling lock, which connects the forward part of the barrel to the bottom carriage, holds the gun steady in transit.

(2) Details

Principle of operation     gas-operated, automatic or single shot
Ammunitionhigh explosive, tracer, and armor-piercing
Type of feed20-round magazine
Length of barrel:
   With muzzle brake57 1/2 in
   Without muzzle brake55 1/8 in
Over-all length of gun with trails folded180 in
Total weight of gun without wheels836 lbs
Maximum horizontal range5,450 yds
Maximum vertical range12,000 ft
Muzzle velocity2,720 f/s
Traverse without wheels360°
Maximum elevation85°
Minimum elevation (depression)-10°
Rate of fire120 rpm
Length of recoiladjustable from 2 in to 2.5 in

d. Operation

(1) Safety. There are two safety features; (a) the lock on the firing handle, to the left and rear of the gun, must be depressed before the handle can be moved forward; and (b) the manual safety mechanism, to the rear and upper right side of the receiver must be turned counterclockwise before the weapon can be fired.

(2) To place the gun in firing position: Set trails and outrigger in the ground. Swing the eccentric (crankshaped) axle so that the weapon is resting on the trails and outrigger, and the wheels are clear of the ground. Then the wheels can be removed by releasing the spring catches, which lock them to the axle.

(3) The elevating handwheel is at the left rear.

(4) To traverse. Traversing can be done by the gunner by putting his shoulder to the shoulder rest at the left rear of the weapon.

(5) To load. Place a loaded magazine into the slot on top of the receiver. The first round can be pushed into the chamber by pulling the handcharging lever into the rear and then forward. (The handcharging lever is at the right of the receiver.)

(6) To fire. Press the lock on the firing handle and move the firing handle forward. Automatic or single-shot fire may be chosen by moving the selector switch at the right rear of the sleigh.

(7) To unload. If there is a misfired round in the chamber, pull back the hand-charging lever in order to extract and eject the round.

e. Ammunition

There are two types of ammunition, high-explosive and armor-piercing.

(1) The high-explosive ammunition has an abnormally large brass cartridge case, and a black projectile body. A green and yellow band are painted together around the middle of the shell, and a red band just below the bourrelet.

The complete round weighs 14.5 ounces, and is 8.187 inches long. The brass nose fuze is point-detonating, bore-safe, and supersensitive. There is a tracer compound in the base of the shell.

(2) The complete armor-piercing round is 8.183 inches long. Both the high-explosive and the armor-piercing rounds are wrapped individually in cardboard containers. The armor-piercing ammunition is packed 70 rounds to a wooden box.

The fuzes for the high-explosive round are wax-dipped, covered with a metal cap, and paper-wrapped. The wrapped fuzes are packed between holes in boards mounted in an unlined crate, and shipped separate from the rest of the round.

f. Maintenance

(1) Oiling and cleaning. This gun should be given the same care as U.S. machine guns and automatic cannon. The bolt parts may be oiled lightly, except in dusty or sandy countries, and then not at all.

(2) Stripping: (a) The barrel is keyed to the receiver by a set screw. When this set screw is loosened, the barrel may be freed by releasing a latch on the rim of the barrel bushing, and turning the barrel about one-sixth of a turn. The gas cylinder yokes will come out with the barrel as one assembly. (b) Place the bolt in the forward position with the handcharging lever. Remove the receiver rear-plate assembly and slide the bolt out to the rear.

g. Accessories

There is a carrying case for the sight, also a small box containing a quantity of headspace washers. The ammunition is carried in a caisson which may be horse-drawn.

The sight-mount carrying case contains the following items: main part of apparatus, glasses, colored glasses, lighting apparatus, rain cover, small camel-hair cleaning brush, towel, oil-can and three brushes.


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