Sunday, 22 May 2016

Imperial Japanese Explosives - Land Mines and Grenades (Part 3)

Imperial Japanese Explosives


Airstrip Mine

Type of Explosive: 31 100kg bombs and picric acid

Method of Detonation: Closing electrical circuit or by use of demolition clock.

Description: The bombs were stacked around picric acid blocks in which electrical detonators were inserted.  The entire mine was under a turf-covered piece of sheet iron that would close the circuit and fire the charge if the iron were lifted or depressed.  A clockwork was also inserted to fire charge if iron was not disturbed.

Improvised Antitank Mine

Type of Explosive: 2 hand grenades, a 2-pound prepared charge of picric acid, and a Mod 99 armor-piercing mine.

Method of Detonation: Pressure on board to fire fuzes in grenades.  Sympathetic detonation relied upon for explosion of main charge.

Description: A prepared picric charge was laid on top of an armor-piercing mine and a hand grenade was set on the two sides.  A board was laid over the top so that pressure would be transmitted to the fuzes of the grenades.

Type JE Antiboat Mine

Diameter: 20 and 1/4 inches
Height: 10.62 inches
Thickness of wall: 3/16 inch
Material of wall: Steel

Weight: 106.5 pounds (not including horns detonator, booster, and wiring)

Weight of filling: 46.5 pounds

Type of filling: Type 98 explosive (HND/TNT N 40/60) with picric acid booster and tetryl detonator.
Description:  This is a hemispherical, chemical-horned, all-welded mine.  The outer body forms a hemisphere and has two handles on its upper portion, a central opening on top to take the booster and safety switch, and two horn openings 180 degrees apart. 

The mine is divided internally into an explosive chamber and a chamber containing booster, wiring, safety switch, and horn electrodes.  The division is made by a shallow, saucer-shaped steel section, which forms less than a hemisphere which is pressed into the outer body from the bottom and welded in place.  A plate is then fitted into the bottom of the mine and is also welded in place.  This last-mentioned plate carries a filling plug in its center and is insert 13/16 of an inch to allow clearance for the plug. 

The horns, two in number, appear to be standard lead-acid mine horns.  They are set at an angle of about 65 degrees and project above the level of the mine top; threads are left-handed.  In the firing circuit is a spring-loaded plunger whose upper end projects through the safety switch cover.  A rubber diaphragm in the top of the cover insures watertight-ness but allows the plunger to move. 

There is a tapered, threaded hole in the center of the top of the plunger and a groove around the plunger near the top.  Until the mine is in position a safety fork engages this groove and holds the plunger up against its spring.  The inner end of the plunger is thus withdrawn from between two contacts in the electrical firing circuit and the circuit is incomplete.

Employment: Used on beaches as an antiboat mine.  It can also be used on land as an antitank mine by burying or otherwise concealing it.

Operation: After the mine is laid the safety fork is removed.  The contact plunger moves down under spring pressure and closes the electrical contacts, thus completing the electrical circuit and the mine is armed.  When a horn is crushed an acid vial inside is broken, allowing the acid to drain down onto two plates of a small battery which generates sufficient amperage to fire the detonator.  As the wiring is series-parallel, either horn on being bent will act independently to fire the mine.

Remarks: The Japanese designation is: Small type land mine.

Type JG Antiboat Mine

Method of actuation: Chemical Horn
Weight of explosive: 22 pounds
Type of explosive: HND/TNT 40/60 (Type 98)

Diameter of top opening: 5.1 inches
Diameter of top: 7 inches
Mine No. --- Diameter of base --- Height --- Total weight
1 --- 14 and 5/16 inches --- 10 and 1/4 inches --- 57 pounds
2 --- 14 and 9/16 inches --- 10 and 5/16 inches --- 55 pounds
3 --- 14 and 9/16 inches --- 10 and 5/16 inches --- 62.5 pounds
4 --- 14 and 5/16 inches --- 10 and 1/4 inches --- 57 pounds
5 --- 14 and 5/16 inches --- 10 and 1/4 inches --- 52.5 pounds
Description:  There are five modifications of the subject mine, each of them being actuated by a single chemical horn screwed into the top.  The mines are either bell-shaped or of a truncated cone shape with an additional distinguishing factor being the location of the welds.  The firing mechanism is similar to the J-XIII; however, a very small detonator is used to initiate the explosive train.
Employment: Used as an antiboat mine for the protection of beaches and reefs; also on land as an A/T mine by camouflaging.

Operation: The mine is laid with the chemical horn installed and a safety pin through the spring-loaded arming spindle.  When positioned properly, the safety pin is removed allowing the spindle to move down and bridge the contacts of the safety switch.

The mine is fired when the chemical horn is crushed or broken.

Remarks: The Japanese designation is: Small type land mine Model 2.


Introduction to Hand, Rifle, and Mortar Grenades

The Japanese armed forces developed, both before and during the war, a fairly extensive line of hand and rifle grenades.  This type of ordnance is primarily used by ground forces, was developed by the Army, but in the peculiar Japanese military organization, was also used by the Navy ground defense units.

The hand and rifle grenades used by the Japanese, although designed for a large variety of purposes, are similar in a number of respects.  Generally, they are smaller than would be considered adequate by American standards.  Also, observation of them in use has shown that, although explosive charges are usually large enough, effective fragmentation is often not achieved.  In the main, the missiles are lacking in safety factors, and in reliability, the principles used in the igniters being of such character that they may be initiated accidentally and are subject to deterioration because of exposure to moisture.  In the case of grenades of glass construction, the danger of initiation is great.

Rifle grenades are often standard hand grenades adapted for use as rifle grenades by the addition of a tail portion.  Hand grenade igniters are retained, with delay trains removed in some cases.  A large variety of improvised grenades has been found in all Pacific areas.  These grenades have been adapted from such items as small ammunition, small bombs, pipe, paper, and wood.  In general, improvisations were the result of shortage of the manufactured item, and were prepared by inexperienced personnel.  Consequently, they were, in almost all cases, very ineffective and extremely dangerous to use.

Type 91 Hand, Mortar, or Rifle Grenade

Overall length: 3 and 3/4 inches
Maximum diameter: 2 inches

Total Weight: 18.8 ounces
Filling: Powdered TNT
Weight of filling: 65 grams
Delay: 6 seconds

-Body: Black
-Fuze cover: Red
-Fuze: Brass

Description: The case iron body is cylindrical and has 50 serrated segments.  A filling plug screws into the upper end of the body, and a brass fuze screws through this lug.  The base of the grenade is threaded, but not entirely through to the charge.  Into these threads fits the propellant container.

The fuze consists of a brass inertia pellet with a steel firing pin separated from the primer by a creep spring.  The inertia weight is held in the fuze by a light brass cap which is crimped into a cannelure in the fuze body so as to prevent the firing pin from reaching the primer.  The firing pin is threaded itno the inertia weight.  In addition, a double brass safety pin fits through the fuze, preventing the firing pin from reaching the percussion cap.

The delay pellet screws into the base of the fuze and contains a small quantity of granular black powder and a pellet of black powder.  A hole drilled in the side of the fuze contains a fusible plug which melts when the black powder burns, allowing the escape of the gases formed on combustion of the delay train.  The tetryl detonator is contained in a brass tube extending from the base of the fuze to the bottom of the bursting charge.

The steel propellant container is screwed into the base of the body.  A perforated plug screws into the base of this container and in a cavity in this is a percussion cap.  Two flash holes lead to a small quantity of black powder.  Inside the propellant container proper is a copper cup containing flakes of nitrocellulose propellant powder.

When this grenade is used as a rifle grenade, a finned tail stabilizer is screws into the base of the grenade instead of the propellant container.

Operation: The firing pin must first be threaded down into the inertia weight.  The safety pin must then be withdrawn.  If the grenade is to be thrown by hand, it is necessary to striker the inertia weight on some hard object to drive the firing pin into the primer to ignite the delay train.

If the grenade is to be fired from the grenade discharger, the grenade with propellant container is dropped base first into the discharger.  When the trigger mechanism of the discharge is operated, its firing pin strikes the percussion cap, igniting the propelling charge which propels the grenade.  Force of setback causes the firing pin in the grenade fuze to compress the creep spring and hit the primer to ignite the delay train.

To fire the grenade from a rifle, the stabilizer is placed over the launcher and the rifle is fired using the special cartridge.  The shock of discharge forces the striker into the primer igniting the delay.

Type 97 Hand Grenade

Overall length: 4 inches
Maximum diameter: 2 inches

Total Weight: 1 pound, 3 ounces
Filling: Powdered TNT
Delay: 4-5 seconds

-Body: Black
-Fuze cover: Red
-Fuze: Brass

Description: The body is cylindrical with serrations to give uniform fragmentation.  This grenade is identical to the Type 91 grenade except that th ebase of this grenade is solid and therefore cannot take a propelling charge.  It can only be used as a hand grenade.

Operation: The firing pin must first be threaded down into the inertia weight.  The safety pin must then be withdrawn.  As the grenade is to be thrown by hand, it is necessary to strike the inertia weight on some hard object thus driving the firing pin into the primer to ignite the delay train.

Remarks: A Type 97 grenade with an aluminum body has been recovered.

A gray or black grenade, which strongly resembles and appears to be a forerunner of the Type 97 grenade, has also be found.  This grenade employs a fuze of black powder rolled in paper leading directly to the black powder bursting charge.  No detonator is used in the firing train.  The fuze pocket is threaded to take a mechanical fuze of the same size as the fuze used in the standard Type 97 grenade.

Next Time: More Imperial Japanese Land Mines, and Grenades

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