Nose Fuze No. 722 Mk III (Service)

Rockets used in

Action

Armed condition

Arming time

Body diameter

Over-all length

Vane span

Color

Description: The fuze consists of a vane cap, fuze body, and magazine. The vane cap is firmly attached to the vane cap hub, which is threaded over a hollow projection on the top of the fuze body. Extending down from the center of the hub is a striker-re-taining pin, which in the unarmed position, forces the striker downwards against its spring. Two small pins are located 180° apart on the outer edge of the hub. In the un-armed position these pins are engaged in two shallow slots in the setback collar.

The setback collar is a brass sleeve fitting around the vane hub and resting on the inertia spring. On the bottom edge of the collar are four studs, which engage in holes drilled in the top of the fuze body when the fuze is unarmed. The tapered top edge of the setback collar is cut away in two places to from two shallow slots and two deep slots, which are connected by a cut-down portion of the collar.

In the lower portion of the fuze body is located a shuttered detonator. This detonator is held offset in the unarmed position by the point of the striker. A magazine adapter is screwed into the bottom of the fuze body, and a thin metal magazine is screwed into the adapter.

Operation: When the rocket is fired, the setback collar moves down against its spring and disengages the stop pins on the hub from the shallow slots. The arming vanes then rotate through an are of 45°, moving the hub around unitl its stop pins come up against the tapered edge of the setback collar. The fuze is held in this position until the expirat-ion of the burning period of the rocket. At this time acceleration ceases, and the setback collar rises, allowing the stop pins on the hub to move into the deep slots in the collar. The collar is allowed to move up far enough to disengage the four studs from the holes in the fuze body. The vanes are now free to rotate both the hub and the setback collar through the remaining 5 or 5½ rotations necessary to arm the fuze. At this point the whole arming assembly falls clear of the fuze.

As the vane hub rises, the striker is forced upward by its spring, eventually removing the point of the striker from the detonator shutter. The shutter spring then aligns the detonator with the striker. On impact, the striker is driven down against its spring into the detonator, initiating the C.E. stemming in the stemmed disc, which in turn fires the C.E. pellet in the magazine.

Remarks: The fuze is fitted with a shipping safety clip (not illustrated), which enga-ges in one of the two drilled holes in the outside of the fuze body and carries a stud which prevents rotation of the arming vanes. The clip is locked in place by a lead seal and is removed manually before the rocket is fired.