Imperial Japanese Army Explosives
Type 3 100kg Skipping Model Bomb
Fuzes: A-8(a); B-8(a)
Overall Length: 53 inches
Length of body: 31 and 1/4 inches
Diameter of body: 9 and 1/2 inches
Thickness of wall: 2/5 inch
Material of wall: Tubular steel
Type of suspension: Horizontal
Suspension lug: Normal Army type hinged suspension lug.
Color and markings: Black overall with a red-tipped nose and a yellow band forward of the suspension lug.
Length of tail: 21 and 3/4 inches
Width of tail: 13 and 1/4 inches
Width of tail fins: 5 and 7/16 inches
Dimensions of tail struts:
-Forward struts: 9 and 7/16 x 1 and 3/16 x 3/32 inches
-Forward struts: 9 and 7/16 x 1 and 3/16 x 3/32 inches
-After struts: 9 and 7/16 x 1 and 9/16 x 3/32 inches
Material: Steel
Type of filling: Paper wrapped cast picric blocks sealed with TNT
Weight of filling: 98 pounds
Total weight of bomb: 220 pounds
Charge/weight ratio: 42.5%
Construction of body: The nosepiece and body are cosntructed of one piece of machined tubular steel. The after end of the barrel is threaded internally to receive the tail assembly. The tail cone is welded to a collar which screws into the after end of the barrel.
Construction of tail: Four tail fins are spot welded to the tail cone. They are braced by two sets of box-type struts. The tail fins are further strengthened by four steel plates welded to the outer edges and running the entire length from the after end to the curved portion of the fins. A round hole is cut in each plate to permit access to the tail fuze pocket.
Remarks: Recent specimens of this bomb incorporate a steel reinforcing section in the after end of the body. This cylindrical section closed at one end by a perforated plate is strengthened by three strips of metal which divide it into six equal compartments. Twelve hexagonal bolts around the outer circumference of the bomb hold the section in place. TNT is cast into the section to a point flush with its after edge.
Remarks: Recent specimens of this bomb incorporate a steel reinforcing section in the after end of the body. This cylindrical section closed at one end by a perforated plate is strengthened by three strips of metal which divide it into six equal compartments. Twelve hexagonal bolts around the outer circumference of the bomb hold the section in place. TNT is cast into the section to a point flush with its after edge.
Type 3 250kg Skipping Model Bomb
Fuzes: A-8(a); B-8(a)
Overall Length: 78 inches
Length of body: 46 and 1/2 inches
Diameter of body: 11 and 3/4 inches
Thickness of wall: 1/2 inch
Material of wall: Tubular steel
Type of suspension: Horizontal
Suspension lug: Normal Army type suspension lug.
Color and markings: Black overall with a red-tipped nose and a yellow band forward of the suspension lug.
Length of tail: 31 and 1/2 inches
Width of tail: 16 and 1/2 inches
Width of tail fins: 8 and 1/4 inches
Dimensions of tail struts:
-Length: 11 and 1/2 inches
-Width: 3/4 inch
-Thickness: 3/32 inch
-Width: 3/4 inch
-Thickness: 3/32 inch
-Material: Steel
Type of filling: Paper wrapped cast picric blocks sealed with TNT
Weight of filling: 230 pounds
Total weight of bomb: 550 pounds
Charge/weight ratio: 41%
Construction of body: A steel nosepiece is welded to a tubular-steel barrel. The after end of the barrel is threaded internally to receive the tail assembly. A row of 12 hexagonal bolts around the circumference of bomb 3 and 1/2 inches forward of the after end of the barrel hold a steel reinforcing section in place. This cylindrical section closed at one end by a perforated plate is strengthened by three strips of metal which divide it into six equal compartments. Twelve holes are drilled in the outer circumference of the section to accommodate the bolts. TNT is cast in the section to a point flush with its after edges. The tail cone is welded to a collar which screws into the after end of the barrel.
Construction of tail: Four tail fins are spot welded to the tail cone. They are braced by a single set of box-type struts. The tail fins are further strengthened by four steel plates welded to the outer edges and running the entire length from the after end to a point just forward of the curved portion of the fins. A square hole is cut in each plate to permit access to the tail fuze pocket.
Type 4 100kg, 250kg, and 500kg Anti-Shipping Bombs
Construction of body: The nose and barrel of the 100kg and 250kg are constructed of 1-piece machined tubular-steel. On the 500kg, a steel nosepiece is welded to a tubular-steel barrel. The after end of the barrel is threaded internally to receive the tail assembly. A row of 12 hexagonal bolts around the circumference of the bomb just forward of the after end of the barrel hold a steel reinforcing plate in place. This cylindrical section closed at one end by a perforated plate is strengthened by 3 strips of metal bent at a 60 degree angle, which divide it into 6 equal compartments. Twelve holes are drilled in the outer circumference of the section to accomodate the bolts. TNT is cast in the section to a point flush with its after edges. The tail cone is welded to a collar which screws into the after end of the barrel. Welded to the apex of the tail cone is a burster tube. This tube contains picric acid and is fitted with a fuze adapter at its after end.
Construction of tail: The tail fins are made from sheet steel. There are two layers of steel in each fin, a single piece having been bent double and the two inner edges welded to the tail cone and burster tube by a continuous weld. The forward and after ends of the fins are closed by welding. The tail fins are not supported by tail struts.
Operation: When the bomb is released the arming wire is withdrawn, allowing the spring-loaded safety pin to fly out, arming the fuze. On impact, the striker compresses the creep spring and hits the primer. The explosion of the primer ignites the first fire charge and the thermite.
Remarks: The suspension yoke will be found on this bomb only when it is suspended from a balloon.
1kg Thermite Incendairy Bomb
Fuzes: Inertia impact fuze
Overall Length: 13 and 1/2 inches
Length of body: 8 and 5/16 inches
Diameter of body: 2 and 1/8 inches
Thickness of wall: 3/8 inch
Material of wall: Magnesium
Type of suspension: Cluster container
Suspension lug: None
Color and markings: Black overall (prime coat of gold paint on the body only)
Length of tail: 5 and 1/8 inches
Width of tail: 2 and 1/8 inches
Width of tail fins: 1 and 1/16 inches
Dimensions of tail struts: 13/16 inch
Material: Light sheet metal
Type of filling: Thermite
Total weight of bomb: 2 pounds 12oz
Construction of body: The bomb consists of a nosepiece, incendiary filled body and explosive filled tail. The nosepiece is made of magnesium and screws into the bomb body. At the flat forward end it is threaded centrally to receive the brass firing pin holder which contains a fixed steel firing pin. At the after end it is pierced by a flash hole. The recess within the nosepiece houses a movable detonator carrier and a creep spring. An off-center transverse safety pin prevents the detonator carrier from hitting the firing pin. The body is a thermite-filled cylindrical magnesium tube. The forward end is threaded internally to receive the nosepiece. The after end is boat-tailed to accomodate the conical tail cone. Three-fourths inch aft of the forward end are four vent holes, 90 degrees apart.
The conical tail cone, made of light sheet metal, slips over the boat-tailed after body of the bomb, and is secured to it by four screws. Each of the three fins, which are made of the same material as the cone, has its inner edge turned and held to the cone by four rivets. Where the three fins meet aft of the apex of the tail cone, they are braced and held together by angular metal strips, which are riveted onto both sides of each fin by two rivets. The outer edge of each fin is turned for a distance of 3/4 inch from the after end. Six rivets hold these turned edges to a circular strut. Filling the inside of the tail cone is a conical cloth bag containing a pyrotechnic mixture which may have explosive properties.
The conical tail cone, made of light sheet metal, slips over the boat-tailed after body of the bomb, and is secured to it by four screws. Each of the three fins, which are made of the same material as the cone, has its inner edge turned and held to the cone by four rivets. Where the three fins meet aft of the apex of the tail cone, they are braced and held together by angular metal strips, which are riveted onto both sides of each fin by two rivets. The outer edge of each fin is turned for a distance of 3/4 inch from the after end. Six rivets hold these turned edges to a circular strut. Filling the inside of the tail cone is a conical cloth bag containing a pyrotechnic mixture which may have explosive properties.
Operation: The fuze is armed when the safety pin is removed. On impact the detonator carrier moves down against the crep spring and hits the firing pin. The resultant flash ignites the thermite filling of the bomb.
5kg Thermite Incendiary Bomb
Fuzes: Mechanical impact tail fuze
Overall Length: 15 and 3/4 inches
Length of body: 6 and 3/4 inches
Diameter of body: 3 and 11/16 inches
Thickness of wall: 1/8 inch
Material of wall: Welded steel tube
Type of suspension: Horizontal
Suspension lug: 3/4 inch steel band secured around the body by a nut and bolt, 5/16 inch hole drilled in the extension of the band to accept metal hook.
Color and markings:
-Bomb Body: Black or olive drab
-Tail: Unpainted tin color
-Bomb Body: Black or olive drab
-Tail: Unpainted tin color
Length of tail: 9 inches
Width of tail: 3 and 11/16 inches
Width of tail fins: None
Dimensions of tail struts: None
Material: Tin-plated sheet steel
Type of filling: Incendiary, consisting of a first fire charge and a main charge
Total weight of bomb: 11 pounds
Construction of body: The bomb body consists of a 1/8 inch thick steel tube welded longitudinally and closed at the forward end by a 3/4 inch thick nose plug which is welded in place. A cylindrical wooden block is fitted part way into the aft end of the body and secured by six countersunk wood screws. The block contains the simple impact fuze and spring-loaded safety pin and also acts as the connecting element between the body and the tail. Two 3/8 inch vent holes are drilled longitudinally through the block 180 degrees apart. The fuze is 2 and 7/8 inches long and has a 1 and 3/16 inch diameter.
The tubular aluminum body contains a striker and a creep spring. A solid threaded plug closes the aft end and a plug containing the primer screws into the forward end. A spring-loaded safety pin holds the striker in position. The incendiary filling in the bomb body consists of a first fire charge which is adjacent to the primer and a main charge below it. The first fire charge is a compressed black powder composed of magnesium, barium peroxide and potassium nitrate. The main charge is thermite.
The tubular aluminum body contains a striker and a creep spring. A solid threaded plug closes the aft end and a plug containing the primer screws into the forward end. A spring-loaded safety pin holds the striker in position. The incendiary filling in the bomb body consists of a first fire charge which is adjacent to the primer and a main charge below it. The first fire charge is a compressed black powder composed of magnesium, barium peroxide and potassium nitrate. The main charge is thermite.
Construction of tail: The tail, consisting of a tinned sheet steel tube closed at the after end, is secured to the wooden block by five wood screws. The tail and body sections rest flush against one another, completely concealing the wooden block to which they are attached. A slot in the tail receives the brass safety pin housing which is contained in the wooden block.
Operation: When the bomb is released the arming wire is withdrawn, allowing the spring-loaded safety pin to fly out, arming the fuze. On impact, the striker compresses the creep spring and hits the primer. The explosion of the primer ignites the first fire charge and the thermite.
Type 97 12kg Thermite Incendiary Bomb
Fuzes: A-2(a) (fitted with a magazine)
Overall Length: 25 and 1/2 inches
Length of body: 14 and 1/2 inches
Diameter of body: 4 inches
Thickness of wall: 3/16 inch
Material of wall: Steel
Type of suspension: Horizontal
Suspension lug: Normal Army type suspension lug on barrel, plus an improvised suspension device described below.
Color and markings: Black overall with a 9/16 inch white stripe just forward of the suspension lug.
Length of tail: 11 inches
Width of tail: 5 and 7/16 inches
Width of tail fins: 2 and 3/16 inches
Dimensions of tail struts:
-Length: 3 and 7/8 inches
-Width: 3/8 inch
-Thickness: 1/16 inch
-Length: 3 and 7/8 inches
-Width: 3/8 inch
-Thickness: 1/16 inch
Material: 1/16 inch rolled steel
Type of filling: Three thermite-filled magnesium fire pots. Two black powder charges
Type of filling: Three thermite-filled magnesium fire pots. Two black powder charges
Weight of filling:
-Fire Pots: 10 pounds
-Black powder charges: 11 ounces
-Fire Pots: 10 pounds
-Black powder charges: 11 ounces
Total weight of bomb: 26 pounds
Charge/weight ratio: 38%
Construction of body: A cast-steel nosepiece is screwed into a tubular-steel body. A normal hinged Army suspension lug and an additional suspension device are fitted to the body. The suspension device consists of two steel bands 11/16 inch wide, each secured around the body by a bolt and nut. The bands are joined by a steel strip 1/2 inch wide which is welded to them. A 1/4 inch steel rod formed into a suspension yoke is welded to the steel strip. A tail cone is welded to a collar which fits into the after end of the body and is held in place by four rivets.
Construction of tail: Four steel fins are welded to the tail cone and are braced by a single row of box-type struts.
Operation: The fuze is armed in flight and on impact the magazine is fired which in turn ignites the black powder charge. The flash from this charge travels down a central flash channel igniting the incendiary composition in the fire pots and firing the black powder charge in the tail. The explosive force of the two black powder charges is sufficient to shear the four rivets at the after end of the bomb body and thus expel the fire pots.
Operation: The fuze is armed in flight and on impact the magazine is fired which in turn ignites the black powder charge. The flash from this charge travels down a central flash channel igniting the incendiary composition in the fire pots and firing the black powder charge in the tail. The explosive force of the two black powder charges is sufficient to shear the four rivets at the after end of the bomb body and thus expel the fire pots.
Remarks: The suspension yoke will be found on this bomb only when it is suspended from a balloon.
Next Time: Incendiary and Smoke bombs, and Parachute Flares
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