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| Japanese Explosive Ordnance – Bombs, Bomb Fuzes, Land Mines,
Grenades, Firing Devices and Sabotage Devices |
| Chapter 2 – Section 2 |
| Navy Bomb Fuzes |
| A-1 (a), A-1 (b) and A-1 (c) Nose Fuzes |
| Bombs in which used: |
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A-1 (a) – Probably interchangeable with A-3 (a). |
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A-1 (b) – Type 99 No. 3 Mk 3. |
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A-1 (c) – Type 98 No. 80 land. |
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No. 80 Model 1 and No. 50 Model 2 ordinary. |
| Japanese designation: |
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A-1 (a) – Type 2 Nose Fuze Model 2. |
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A-1 (b) – Type 90 Nose Initiator. |
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A-1 (c) – Type 2 Nose Fuze Model 1. |
| A-1 (a) | A-1 (b) | A-1 (c) | ||
| Color | Natural brass | Natural brass | Brass upper body. Lacquered lower body. | |
| Over-all length | 6 inches | 6 inches | 7 5/8 inches | |
| Over-all width | 2 1/4 inches | 2 1/4 inches | 2 5/16 inches | |
| Material of construction | Brass | Brass | Brass except for steel set-screw, striker point and locating pin. |
| Position and method of fixing in bomb: Threaded into nose bomb. |
| A-1 (a) | A-1 (b) | A-1 (c) | ||
| Components of explosive train | Standard Navy gaine. | Primer and det- onator. | Standard Navy gaine. | |
| Fuzes likely to be found with | Navy tail fuzes except C-1 (a) | Possibly D-2 (b) | B-3 (b) or possibly B-2 series. |
| Delay times: Probably none. |
| Threads: All three fuzes 1 7/8 inches in diameter, 10 threads per inch. |
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Description: The upper portion of the body houses the vane boss which secured by re-training pins and is free to rotate. It is threaded into the lower body and held by a grub screw. Through the upper and lower bodies passes the striker threaded to the anvil turns when the vane boss is rotated and threads up the striker until the keys shoulder in the partial keyways. Through the striker passes a shear wire which breaks on impact and a locating pin which slides out of a slot in the upper body on impact. |
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Operation: On release, the arming pin are pulled out, the vanes and vane boss turn the anvil which threads upward and away from the fuze (due to left-hand threads). The va-nes do not come off because the vane boss to which they are attached, is held by retai-ning pins and can only rotate. The anvil is stopped by keys when it reaches the limit of its partial keyways. Impact pushes anvil back. Spindle is forced downward. Shear wire is sheared, and the firing pin impinges on the primer. |
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Remarks: A-1 (a): May arm in 5 revolutions of the arming vanes. |
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A-1 (b): This fuze was used in a 32-kg bomb employed as an antivehicle mine in beach defenses against landing forces attempting a seaward invasion. |
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A-1 (c): This fuze is similar to the A-1 (a). It differs in that the fuze body below the thread is substantially longer while the fuze body above the threads is only slightly longer than that of the A-1 (a). The striker spindle is longer, the diameter of the anvil head is larger, and the arming vanes are longer. |
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Figure 114 – A-1 (a), A-1 (b), and A-1 (c) Bomb Fuze. |
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