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.
2. TABLE OF CHARACTERISTICS
|Weight|| ||840 lbs|
|Elevation||-9° to +81.9°|
|Traverse (pintle type)||360°|
|Maximum horizontal range ||5,450 yds|
|Maximum vertical range||12,000 ft|
|Rate of fire||120 rds per min|
|Muzzle velocity||2,720 fs|
|Length of barrel||70 calibers|
3. DESCRIPTION OF COMPONENT PARTS
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).|
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.
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.
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.
4. NOTES ON OPERATION
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
(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.
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