German Fuze A.Z. 23 umg. 0.15German Mechanical Time and Percussion Fuze S/90 K (Dopp.Z. S/90 K)
(Fig. 7)

This igniferous nose fuze, used with a gaine in the H.E. bomb fired from the 20 cm light spigot mortar, is designed to arm in an unrotated projectile and has a combined graze and direct action with an optional delay. The arming device is operated by the burning of a delay composition which is ignited by a second detonator and delays the arming for a period of approximately 0.6 of a second after firing.

The body of the fuze is alumnium alloy with a flat topped conical head which has the usual metal sealing disc at the top and is fitted with a safety pin secured by a lead seal. The abbreviated designation "Wgr.Z. 36" is stamped near the lower part of the coned head. On the opposite side of the head there is a delay setting plug inscribed with an arrowhead. Stamped in the head at one side of the plug is a graduation lettered "M". On the opposite side a similar graduation is lettered "O". The arrowhead is set to the "M" graduation for delay or the "O" graduation for non-delay action.

The weight of the fuze is 6 oz.

The fuze body is recessed at the top to receive the needle pellet and safety arm and screwthreaded internally for the insertion of the closing cap. At the base of this recess four vertical recesses are formed. The central and largest recess contains the steel graze pellet and has two flash channels at the base. One of these channels is central, the other is displaced from the centre and is inclined. Of the other vertical recesses, two are formed side by side and are connected near the base ends by an inclined flash chan-nel, which continues to the exterior of the body where it emerges at the screwthreaded protion and is closed by a screwed plug. One of these recesses contains a brass deto-nator pellet carrying a No. 37 igniferous detonator, the pellet being supported above a steel needle by a spiral spring and safety pin. The pin is inserted through the head of the fuze and engages in a circumferential groove in the side of the detonator pellet. This re-cess is closed at the top by a screwed plug. The connected vertical recess contains, at its lower end, two small pellets of delay composition beneath a sleeve filled with a similar composition. An inclined channel leads from the base of the recess to the head of the fuze where it is lightly closed by a metal disc secured by stabbing. The sleeve is of alu-minium or aluminium alloy and is screwthreaded externally for insertion in the recess. A detent positioned above the sleeve is supported by the delay filling contained in the sleeve. The detent has a collar formed around its centre which supports a spiral spring held under conpression between the collar and a screwed ring at the top of the recess. The upper end of the detent passes through the screwed ring and retains the safety arm in the safety position, i.e. partly covering the central recess which contains the graze pellet and closing the fourth recess. The fourth vertical recess has a channel at its base leading to a radial channel containing the shutter bolt in the lower part of the fuze. This recess contains a locking bolt for the shutter. The bolt is supported by a spring and has a collar formed near its head. The collar is engaged by an eccentric projection on the in-ner end of the delay setting plug which is contained in a radial channel in the head of the fuze. When the plug is set to the "M" graduation the eccentric projection, bearing down on the collar, pushes the locking bolt down into the shutter bolt channel and prevents the bolt moving outwards. When the plug is set to "O" the eccentric projection is raised and the locking bolt is free to be raised clear of the shutter bolt when the safety arm moves clear of the recess. The safety arm, in the form of a curved aluminium arm, is pi-voted at one end where a spring is fitted which tends to swing it clear of the path of the graze and needle pellets and clear of the recesses containg the locking bolt.

The lower part of the fuze contains the shutter assembly, the delay holder and a maga-zine of gunpowder. The shutter assembly consists of a copper shutter attached to an aluminium bolt and a spiral spring which is fitted to the inner end of bolt and is under compression when the shutter is held in the closed position by the locking bolt. The de-lay holder is of the usual type used in German fuze and is in the form of a solid aluminium cylinder with a central flash channel with a groove for the shutter above it and a displa-ced channel containing delay composition. A perforated tin disc is placed over the holder and the shutter. The magazine screwed into the base of the fuze is in the form of cup shaped closing plug with a central flash hole and contains a perforated pellet of gun-powder. The flash hole is closed by a paper disc on the inner side.


The safety pin is removed and the fuze set for delayed or non-delayed action before firing. If set for "delay" the locking bolt is held down to engage the shutter bolt by the eccentric projection on the setting plug. If set for "non-delay" the locking bolt is held down only by the safety arm.

On acceleration, the detonator pellet in the side recess sets back compressing its spring, and the detonator is pierced by the needle. The flash passes through the connecting channel into the recess containing the delay composition and the detent. The pressure set up by the burning of the delay composition escapes by the inclined channel leading to the exterior of the head of the fuze. When the delay composition supporting the spring loaded detent has been destroyed, the detent is forced down by its spring and the safety arm is thus released. The arm is then swung clear of the graze and needle pellet and the recess containing the locking bolt by its pivot spring. It set for "non-delay" the locking pellet is then free to be raised by its spring and the shutter is released to be pushed out by its compressed spring to the open position. If set for "delay" the locking bolt cannot rise as it is held by the projection on the setting plug and the shutter re-mains closed leaving only the delay channel in the holder exposed. Forward movement of the graze pellet during the period of deceleration is prevented by the creep spring.

On graze the pellet overcomes the spring and carries the detonator on to the needle. When suitable impact is obtained, the needle pellet is driven in at the same time as the pellet moves forward and direct action results. The path of the flash from the detonator to the magazine is governed by the setting. If set for "delay" the central channel in the delay holder is closed by the shutter and the flash can pass only through the channel containing the delay composition. If set for "non-delay" the central channel is exposed and the flash passing by this route will be the first to reach the magazine.

Detonator and Delay Compositions

The detonator carried in the graze pellet is No. 26 which is in common use in German fuzes. The No. 37 detonator contained in the side recess has a layer consisting of mer-cury fulminate, potassium chlorate and antimony sulphide over a filling of black powder.

The delay composition in the sleeve supporting the detonator and the pellets beneath the sleeve consist of the following:–





3.9 per cent

2.7 per cent

Red lead

75.5 per cent

72.0 per cent


20.6 per cent

25.3 per cent

The delay composition used in the channel in the delay holder has been found to be gun-powder in a fuze dated 1940. In a fuze dated 1941 a composition similar to that in the sleeve and pellets has been found. This composition has also been found in the delay holder of the A.Z. 35 K fuze described in Pamphlet No. 11.

Fig. 7

German Fuze A.Z. 23 umg. 0.15German Mechanical Time and Percussion Fuze S/90 K (Dopp.Z. S/90 K)