Monday, 9 May 2016

Imperial Japanese Explosives - Land Mines and Grenades (Part 1)

Imperial Japanese Explosives


Although the use of land mines by the Japanese forces was not as extensive as it was in Europe, land mines were important defensive weapons in the Pacific war.  Also, because of the Japanese lack of effective anti-tank artillery and the inequality of armored forces which was everywhere existent, mining and similar tactics became a mainstay of defense against mechanized equipment.  This was more apparent as Allied forces approached the Japanese homeland, and the defense forces were better equipped than those in the outlying islands had been.

Three features of the Japanese land mining methods were especially important.  The first was the relatively small number of standard, mass-produced mines and firing devices.  This lack of variety in standard mines led to a large amount of field improvisation of land mines and other defense devices, using ordnance and other types of explosives originally designed and manufactured for other purposes.

The second outstanding feature of Japanese land mining was the prevalent use of extremely large charges for all types of land mines.  Bomb, sea mines, depth charges, and even torpedo warheads were used extensively with all types of detonating equipment.  The use of these large charges, although it was wasteful, was the result of inability to use heavy explosive ordnance for its intended purpose, and rendered the potential danger area of land mines very great.

The third was the emphasis which was placed on various types of controlled mines.  This tendency was in keeping with the use of improvised mines, controlled mines being much easier to improvise than enemy activated mines.  Controls ranged all the way from elaborate electrical systems to crude, hand-operated, suicide devices.  Firing devices operated by simple lanyards or poles were common.

Japanese mining techniques were characterized by an almost complete lack of uniformity.  Land mining policies seemed to have been formulated by local authorities and indicated that little or no information was available, and that training was inadequate.  Thus, the Japanese land-mining program was far from being as effective as it should have been tactically and did not often cause serious difficulty to advancing Allied forces.

Type 93 Antitank and Antipersonnel Land Mine

Diameter: 6 and 3/4 inches
Overall Height: 1 and 3/4 inches

Weight: 3 pounds
Weight of explosive: 2 pounds
Type of explosive: Solid ring main charge of cast picric acid with inner ring booster of pressed powdered picric acid containing a central hole 5/8-inch in diameter to house fuze.  Explosive completely covered by layer of paper, shellacked to the explosive and waxed externally.
Color and markings: Olive drab with narrow red ring around brass plug.  Mine may have numerals (such as 16.9) in white on top indicating date.

Meaning safe inscribed on top of safety cap and on lug of safety washer.

Description: The mine is circular with a slightly domed top and flat bottom.  It is constructed of an upper and lower section of sheet metal secured together by four heavy corrugations in the walls which serve as threads.  The overlap of the walls of the two sections is sealed with a bituminous paint.  The interior of the container is painted with a black enamel.  Soldered on the inside of the bottom of the lower section is a brass disc 1 and 9/16 inches in diameter, having a threaded collar for the insertion of the fuze.

The central hole in the upper section is reinforced with a brass collar threaded to receive the brass plug.  A thin leather washer fits between the brass plug and the collar to seal the mine.

Two brass rings are fastened to two opposite sides of the upper section by means of a soldered metal strip.  Drag ropes may be fastened to the rings.

The fuze assembly consists of a striker held under spring pressure by a shear wire, a percussion cap, a primary detonator, and a larger secondary detonator all incorporated in the fuze body which is threaded on the lower end to screw into the collar in the bottom of the mine. 

A safety cap is screwed into the upper end of the striker until the mine is laid.  An additional safety feature is a brass cylinder with attached washed which fits over the brass safety cap and rests on top of the fuze body, the washer fitting under the leather washer of the brass plug.
Employment: Antipersonnel and antitank.  The Japanese have two sizes of shear wire for this mine.  One for antipersonnel use shears at 70 pounds, the other, for antitank use shears at 250 pounds.  These mines have been found buried upside down with additional explosives placed beneath them to increase their effect.  The A/P fuze has a black upper body.
Operation: With the safety devices removed, any load on the cover of the mine causes the brass plug to press down on the striker.  If the pressure is sufficient, the shear pin is sheared.  This frees the striker which, under pressure of the spring, strikes the percussion cap initiating the detonating system.

Anti-Vehicular "Yardstick" Land Mine

Overall length: 36 inches    
Diameter: 3.35 inches by 1.8 inches (oval)

Total weight: 10 and 1/2 pounds
Weight of filling: 6 pounds
Weight of each explosive block: 3/4 pound
Type of explosive: Eight identical blocks of picric acids cast in paper container, coated with paraffin.  Each block molded on one end to take fuze so that two blocks placed with molded ends together completely enclose fuze.
Color and markings: Mine case painted olive drab over undercoat of black.  Interior painted with black lacquer.


(fuze top portion) stenciled vertically in red characters approximately 7/8-inch tall on one side, and the corresponding marking

(fuze bottom portion) in smaller characters about 1/2-inch tall stencilled on reverse side.
Description: The mine is an oval tube formed by two halves of sheet steel welded together with continuous welds and closed at both ends by steel caps held in place by single screws.  One of the caps has a hole to take the safety wire, which is a single wire extending the length of the mine and passing through all the fuzes.  A spring clip holds the safety wire in place.

The explosive blocks flattened on one side do not completely fill the mine case.  The space left between the flat side of the blocks and the wall of the case accommodates the protruding heads of the fuzes and also allows space for the side of the case to be depressed on the fuzes by the passage of a vehicle over the mine.

The fuze consists of a short, cylindrical body which houses the striker release plunger, the striker housing which contains the striker and striker spring, and the gaine.  The gaine and striker housing are identical in external appearance and screw into the sides of the cylindrical fuze body in diametrically opposite positions.

The striker release plunger is a split pin with an enlarged flat head.  It is positioned in the fuze body by a copper shear wire.  A second hole 90 degrees from the shear wire hole accommodates the safety wire.  The lower end of the plunger is split by a slot, the width of which is increased on the inner end.

Employment: This mine is used as an anti-vehicular mine.

Operation: After the safety wire is removed and burying plug is screwed in, the mine is buried.  A vehicle passing over will crush the case and thereby apply enough pressure on the top of the fuze to break the shear wire and depress the striker release plunger.  As the enlarged portion of the slot comes opposite, the spring-loaded striker moves across through the opening and into the primer cap.

Type 99 Armor-Penetration Land Mine

Overall Length: 4.75 inches (circular)
Overall width: 1.5 inches
Total weight: 2.5 pounds
Weight of filling: 1.5 pounds
Fuze delay: 8-10 seconds

Type of explosive: Eight cast blocks, 50-50 RDX-TNT shaped to form circle. Individual blocks wrapped in wax paper.
Color and markings: Khaki.

Stenciled in black on body

Stencilled on opposite side
Description:  The mine resembles a canvas cloth bag, disc shaped, with a snap-fastened flap on the outer edge for inserting the eight blocks of explosive.  Opposite the filling flap on the outer edge of the mine, is a metal adapter which is externally threaded to receive the fuze. 

Four equally spaced permanent magnets are attached by khaki webbing to the outer edge of the mine body.  The mine is packed two to a wooden box complete with wooden shipping plugs in the fuze adapters.  The fuzes are enclosed in tubular metal cases sealed with a paper band and tear string.  For carrying on the field, the mines are packed individually in a khaki-colored cloth pouch. 

The fuze contains two springs, a compression spring and a firing pin spring, the latter of which is contained in a firing pin sleeve.  Four steel retaining balls fit into holes in the firing pin sleeve and notches in the firing pin, retaining the position of the firing pin.  A fuze cap provides a base for the first spring and is grooved on the inside about one-third of the way up from its base. 

There is a safety pin which passes through the fuze body just below the base of the safety cap and between the striker and the percussion cap.  The powder delay train threads into the base of the fuze body, and the detonator tube threads over the base of the delay train container.

Employment: Used as antitank or antivehicular mine, or against armored fortifications.

Operation: The fuze is carried separately and is secured to the mine by a locking ring.  In use, the safety pin is pulled, the fuze cap given a sharp rap, and the mine either placed on or tossed on armor plate within a range of ten feet. 

When the fuze cap is forced downward against the compression spring, its groove aligns with the retaining balls.  The tension of the firing pin spring forces the retaining balls into this groove and also forces the striker down onto the percussion spring.

Remarks: Test detonations of this mine indicate a distinct "Monroe Effect" at the junction of the inner edges of the explosive blocks.  One mine will produce complete perforations in plate up to 1 inch thick.  The mines are frequently coupled together and when so used, will penetrate 1.5 inches of steel plate.

Lunge Mine

Overall length: 78 inches (including handle and legs)
Total weight: 14.3 pounds (mine body and handle)
Length of body: 11.6 inches
Diameter at base: 8 inches
Weight of body: 11 pounds (including explosive)

Length of handle: 59 inches
Diameter of handle: 1 and 1/4 inches
Weight of handle: 3.3 pounds
Explosive filling: Crude TNT

Weight of filling: 6.6 pounds
Description: The mine consists of a conical shaped hollow charge, with a wooden handle at the apex of the cone and three metal legs welded to the base.

The conical charge is housed in a steel container.  Fitted into the base of the charge is a hollow, truncated cone designed to give the mine the increased power of penetration of this hollow charge.  A well in the apex of the charge contains the detonator.

The wooden handle has a steel striker fitted in one end.  This end is encased in a metal cylinder and is held there by a safety pin and a copper shear wire.  The cylinder is attached to the neck of the charge container by a threaded connecting ring.

Three metal legs 6 inches long are welded to the base of the charge container at 120 degree intervals.  They guarantee the proper stand-off to obtain the maximum effect from the hollow charge.

Employment: Used as an antitank weapon.  Capable of penetrating 6 inches of steel plating.

Operation: The operator pulls out the safety pin, then uses bayonet tactics, the left hand at the center of the handle, the right hand at the after end, as he lunged forward.  When the legs of the mine strike the target, the handle is driven forward breaking the shear wire, and the striker is driven into the detonator initiating the explosion of the mine.

Suction-Cup Mine

Overall length: 66 and 3/8 inches (including handle and cups)
Total weight: 7 pounds, 8 ounces (mine body and handle)

Length of body: 5 and 5/16 inches (including cups and handle holder)
Diameter of body: 4 and 3/8 inches
Weight of body: 5 pounds, 8 ounces filled (including suction cups)

Total length of handle: 59 and 5/8 inches (2 pieces)
Diameter of handle: 1 and 7/16 inches

Explosive filling:
-RDX: 53%
-TNT, 47%

Description: The mine body is made of a black, sheet metal, longitudinally welded, cylinder, having a flanged metal cap spot-soldered over each end.  Soldered to the circumference of the forward end, 180 degrees apart, are two metal loops.  Into each loop is fitted a solid rubber plug, the forward end of which is made into a shallow suction cup.  These suction cups are held in place by metal pins and extend just forward of the leading edge of the mine body.

A wooden handle, consisting of two pieces held together by a metal sleeve, fits into a hollow extension welded to the top of the mine body.

The initiating element, consisting of pull igniters, safety fuse, prima cord, and blasting caps, is rigged in duplicate and extends the length of the handle into a well in the top of the mine body.  Four blasting caps are used, two being crimped to the forward end of the safety fuse and two being crimped to the forward end of the prima cord. 

If only one section of the handle is used the prima cord may be omitted; in which case the blasting caps of the safety fuze are place directly into the well of the mine.  The initiating element is lashed to the handle of the mine with light line.

Employment: These mines are known to have been successfully used against parked aircraft.

Operation: The suction cups hold the mine in position when it is placed against a smooth surface.  The friction igniters are pulled simultaneously, starting the safety fuze burning.  This gives an estimated delay of 10-15 seconds, after which the upper blasting caps, the primacord, the blasting caps in the charge, and the main charge are initiated in sequence.

Dutch Antitank and Antipersonnel Land Mine

Overall height: 3 and 1/2 inches
Height of body: 2 and 7/8 inches
Diameter of body: 8 and 1/8 inches
Diameter of cover: 8 and 1/4 inches
Wall thickness: 5/32 inch

Weight of filling: 5 and 1/4 pounds
Total weight: 9 and 1/2 pounds
Type of filling: TNT

Color and markings: Olive drab overall with "P.W. 2-41" in red across top of both cover and mine body.  "P.W. 2-41" inscribed on the fuze head.

Description: The body is of pressed steel construction with a crimped-on base.  The cover is also pressed steel with four side slots corresponding with screw holes in the body which take the small fixing studs.

In the center of the cover is a brass plug.  A helical spring holds the cover away from the body.  The igniter and detonator assembly screws into the top of the body of the mine.  The striker is spring-loaded and is held off the cap by the 1/16-inch diameter, soft copper shear wire.  There is no safety pin.

The detonator assembly consists of a detonator tube enclosed by an outer tube, and a primer.

Employment: The Japanese use the mine mainly against personnel, laying them in narrow trails, on beaches, and at entrances to bivouac areas.  Normally they lay it on top of the ground.

Operation: The movement of the cover is regulated by the size and position of the slots.  Pressure on the cover is transferred from the brass plug on to the striker head, thus shearing the shear wire and allowing the spring to drive the striker into the cap thereby detonating the mine.

A load of 50 pounds is sufficient to shear the copper shear wire.

Next Time: More Imperial Japanese Land Mines, and Grenades

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