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Japanese Explosive Ordnance – Bombs, Bomb Fuzes, Land Mines,
Grenades, Firing Devices and Sabotage Devices |
Chapter 2 – Section 1 |
Army Bomb Fuzes |
Type 4 - Two-Second Delay Fuze A-8 (a) |
Bombs in which used: Type 3 100-kg. skipping model bomb. |
Color: Brass, except for black vanes. |
Overall length: 3 1/2 inches (less booster and gaine). |
Overall width: 1 1/2 inches. |
Material of construction: Brass except for steel arming vanes, tightening pins and firing pin. Tinned sheet steel booster housing. |
Position and method of fixing in bomb: Screwed into nose of bomb and tightened by a wrench that fits over the protruding pins. |
Components of explosive train: Primer, delay gaine, and booster. Relay incorporated in gaine. |
Fuze likely to be found with: B-8 (a). |
Delay time: 2 seconds. |
Threads: 13 threads per inch; RH, diameter 1 5/32 inches. |
Description: The fuze body houses a spindle that has a firing pin at its lower end, and a threaded segment at the upper end that protrudes above the body. The vane assembly consisting of four black vanes attached to a brass hub screws into this threaded portion. The central segment of the spindle is enlarged to form a shoulder for a rubber gasket lo-cated in a recess in the top of the fuze body. A brass washer threads into this hole and bears on the top of the gasket. The spindle is drilled to receive a brass shear wire 2.5 milimeters in diameter. |
The primer is contained in a thin cylinder pressed into the lower fuze body against a divi-ding section. The section is pierced with a flash hole. |
The delay element, consisting of a column of pressed brown powder, is carried in a brass piece which threads into the base of fuze body and aligns with the flash hole in the base of the dividing section. |
The gaine threads into the base of the fuze immediately below the delay element. It has a relay pellet above a lead azide cone imbedded in cyclonite. |
The booster, containing two cyclonite pellets, is housed in a light metal cylinder which is crimped onto a groove in the lower part of the fuze body just below the threads. |
Operation: The safety fork is withdrawn allowing the vanes to rotate up the threaded spindle and fall clear. On impact with a solid target the shear wire is sheared and the firing pin is driven into the primer. The flash ignites the delay train which in turn fires the gaine. |
Figure 100 – A-8 (a) Bomb Fuze. |
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