EMPLOYMENT: Used in 15-cm H.E. projectiles.

DATA:

Over-all length: 3.125 inches.

Maximum diameter: 2.312 inches.

Threaded length: 0.5 inch.

Number of threads: 4 RH.

DESCRIPTION: The A.Z. 23 umg fuzes differ externally from the A.Z. 23 fuzes in having a much shorter coned head and are longer between the flange and the base. This lower part, which enters the fuze hole in the projectile, has only a few screw-threads below the flange, the remainder being plain. Three types of the "umg" fuze have been found. These are:

A.Z. 23 umg 0.8

A.Z. 23 umg m. 2 V

A.Z. 23 umg 0.15

The "m. 2 V" fuze is also an optional delay fuze with two alternate delays. Details of the fuze are not yet available. Both this and the "0.8" fuze are being replaced by the "0.15" fuze.

The "0.15" fuze with an optional delay of 0.15 of a second is here described and differs from the later type of "0.8" fuze only in the time of the delay.

Each of these fuze can be identified by the designation stamped above the flange.

CONSTRUCTION: The A.Z. umg 0.15 has the usual combined D.A. and graze mechanism consisting of a steel graze pellet carrying the detonator and an aluminum striker pellet held apart by a creep spring and five brass centrifugal segments encircled by an expand-ing spring ring. (See fig. 578.) The graze pellet is contained in a central recess in the body which has two flash channels at the base. One channel leads direct to the maga-zine through an open channel in the delay holder, the other leads to the magazine through the delay composition in the delay holder. The striker pellet with a steel sleeve surrounding it and a wooden hammer above it is carried in the  head of the fuze. The steel head is retained in the body by a retaining ring which screws into the top of the body and engages an external flange near the lower part of the head. The circumferent-ial rim at the bottom of the head varies in depth to act as a cam which positions the spring loaded locking bolt of the shutter. Thus, when the head is rotated to bring the deepest portion of the rim over the locking bolt, the bolt is pressed down into the radial recess containing the shutter in the lower part of the fuze and prevents the shutter from opening. The setting positions of the head are marked on its protruding part by two lines at right angles which are set to an index line on the retaining ring and body. The setting line for delayed action is marked "MV" and that for nondelay "OV".

The delay holder, shutter assembly and magazine are all of the same type described for other fuzes of the A.Z. 23 type.

ACTION: The fuze is set for "delay" or "nondelay" by turning the head to bring the appro-priate setting marking into coincidence with the index line. When set to MV the locking bolt is pressed down by the deep part of the rim at the bottom of the head and locks the shutter in the closed position. When set to OV the short part of the rim is over the lock-ing bolt thus, permitting the bolt to be raised clear of the shutter recess by its spring.

During flight, the coil of the expanding spring ring is enlarged and the segments swung clear of the graze pellet by centrifugal force. If set of "nondelay" the shutter is also thrown outwards and the open flash channel in the delay holder is exposed. Forward mo-vement of the graze pellet is prevented by the creep spring.

On graze, the detonator is carried forward by the graze pellet and pierced by the striker. When suitable impact is obtained, the hammer and striker pellet are driven in as the gra-ze pellet moves forward, thus accelerating the action. With the head set for "nondelay" the flash from the detonator passes direct to the magazine. If set for "delay" the open channel in the delay holder is masked by the shutter so the flash has burn through the delay composition to reach the magazine.

Figure 578 – A.Z. 23 umg