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| BRITISH EXPLOSIVE ORDNANCE |
| Part 4 - Chapter 2 |
| Rocket Nose Fuzes |
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Nose Fuze No. 721 Mks II, II*, and III (Service) |
| Data |
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Rockets used in |
Shell, H.E., 3-in., 29-lb., Mk I, and Shells, Incendiary and Smoke, 5-in., Mk I |
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Action |
Instantaneous on impact |
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Armed condition |
No external evidence |
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Arming time |
Instantaneous |
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Body diameter |
2.33 in. |
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Over-all length |
6.4 in. (with cap and magazine) |
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Color |
Safety cap, unpainted alloy; body, black; magazine, brass |
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Description: This fuze is a simple impact fuze consisting of a striker and an attached pressure plate, which is held away from the detonator by a thin aluminum shear wire. A safety cap is screwed over the head of the fuze, and the sides of the safety cap hold a safety clip in position beneath the pressure plate of the striker. The safety cap consists of two metal segments riveted one at each end of a short strip of spring steel. |
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The detonator is carried in a brass detonator holder screwed into the underside of the body. The channel in the bottom of the detonator holder is stemmed with C.E. Above the holder, interposed between the detonator and the striker, is a small brass retaining disc suspported on a washer of similar material. |
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The magazine consists of a brass cup crimped to the body of the fuze. |
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Operation: Before firing, the safety cap is removed, and the safety clip is ejected. The safety cap is then replaced, insuring that the round will not fire on water impact. On impact with a hard surface, the safety cap is crushed, and the pressure plate drives the striker through the shear wire and into the detonator. |
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Remarks: Fuzes No. 721 Mks II* and III differ from the Mk II only in that a solid horseshoe-shaped metal safety block replaces the spring safety-clip assembly. |
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It should be noted that an unexploded round found with the safety cap in position is by no means to be considered safe, as the safety cap is replaced after the safety clip has been removed. |
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| Figure 224 – Nose Fuze No. 721 |
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