Nose Fuze No. 873 Mk I (Service)

Description: The vanes and vane cap of this fuze are of unpainted steel. The five vanes are cut out of one piece of sheet steel and soldered onto the cap. In the top of the cap is a small stop pin on the fuze body to prevent the cap from being screwed down too tightly. The vane cap threads all the way down the fuze body. In the upper part of the fuze body is a sheet-metal diaphragm with a needle striker soldered to its center. This rests on a shoulder in the fuze body and is covered by a sheet-steel retain-ing disc in which seven holes are drilled to allow air passage. The retaining disc in this fuze is staked in place. In the lower fuze body is a detonator shutter moving in a cham-ber at right angles to the striker. In the unarmed position the shutter is out of line, and the detonator is lined up under a safety flash hole. On one end of the shutter is the shutter spring. On the other end is a detent, which holds the shutter out of line. The de-tent rests in a hole that leads to the outside and is held in the shutter chamber by a steel clip which rests in a longitudinal groove along the outside of the threaded fuze body. This clip is pivoted on its lower end, and there is continual pressure exerted on it by the detent, which, in turn, is being forced out by the shutter and shutter spring. Be-low the detonator is a flash channel leading to the magazine. Around the lower fuze body are a leather washer and a spring locking ring.

Operation: When the bomb is dropped from the plane, the safety wire is pulled out and the vanes and vane cap are free to rotate. After about 11 revolutions of the vanes, the vane cap releases the steel clip in the fuze body, allowing the clip to be pivoted down by the detent under pressure of the shutter and shutter spring. The detent is thus forced out of the fuze, and the shutter is allowed to align itself with the striker.

Remarks: This fuze is designed to give aerial burst functioning on all but the first bomb of a stick or cluster. The first bomb explodes on impact, and blast pressure from its explosion snaps the diaphragm of the fuze in the bomb next above it. Blast pressure from the explosion of the second bomb fires the third, etc., giving a "stepped" explosion effect to the whole stick or cluster.

Figure 171 - Nose Fuze No. 873 Mk I