The German percussion fuze AZ. 23 Rh.S. with 0.25 second delay (Fig. 5) is used in the 105 mm howitzer and probably also in 75 mm separate ammunition. It is designed to function on impact or graze.

The fuze consists chiefly of a body, needle and needle pellet, centrifugal bolts with spring, detonator pellet with detonator, creep spring, delay mechanism and magazine.

The body of aluminum, is in two parts, screwed together and secured by a set screw. The upper part has a central channel throughout its length to receive the needle, which is secured in the aluminum needle pellet by a securing screw. The needle is fitted with a wooden extension. On the underside of the needle pellet, the central channel is enlarged to house five brass centrifugal bolts, each with its pivot pin. The bolts are kept pressed towards the centre of the fuze by means of a phosphor bronze spring, which maintains the bolts in such a position that when the fuze is at rest, the needle cannot pierce the detonator.

Fig. 5

The lower part of the body contains a brass detonator pellet and detonator, the delay mechanism and a magazine. The detonator is secured in the pellet by a screw having a central fire channel. Four radial slots are cut on the underside of the pellet to ensure that the flash from the detonator reaches the delay channel.

The delay mechanism consists chiefly of a delay holder, index plug with centrifugal bolt and spring, and a copper plate. The holder is pierced by two channels, one central and empty, the other eccentric and carrying the delay. On the upper portion of the holder a recess is cut in which a copper plate can slide. According to its position this plate covers or uncovers the central channel.

The index plug is secured in the body of the fuze by a screwed collar. A cylindrical cavity is formed in the plug to receive the centrifugal bolt with spring and a recess is cut in the plug to receive the copper plate. On the outside of the plug a slot is cut which serves as an index for setting the delay mechanism. If the plug is set in the delay position, the re-cess does not coincide with the plate, the latter therefore remains in the closed position masking the central fire channel. If the fuze is set to the instantaneous position (Fig. 6) the recess is in line with the plate and the latter is free to move outwards under centri-fugal force and so un-mask the central fire channel. A brass plate with holes bored to correspond with the delay and central channel is placed on the delay holder and forms an upper bearing surface for the copper plate.

The bottom of the fuze is closed by the magazine, having a central fire channel, which is screwed in and retains in position the delay holder.

Action.

Before firing (Fig. 5) – The needle is separated from the detonator by the centrifugal bolts which are retained in the closed position by their spring. The copper plate of the delay mechanism closes the central fire channel by the pressure from the centrifugal bolt. This position is maintained whether the fuze is set delay or instantaneous. The de-lay channel is always uncovered.

Thus, even if a failure of the safety arrangements occur and the needle pierces the de-tonator or the detonator itself fires, the fuze can only function with delay; the shell, therefore, cannot burst at less than 0.25 second's time of flight from the muzzle.

To set the fuze for instantaneous action the slot in the index plug is turned to a position parallel to the axis of the fuze bringing the recess in the plug opposite the copper plate (Fig. 6). For delay action the slot is turned at right angles to the fuze axis opposite the marks M. and V.; in this position the plug retains the copper plate in the closed position (Fig. 5).

After firing. – The centrifugal bolts swing outwards overcoming the spring thus leaving the needle and detonator pellets free to move towards each other. The creep spring pre-vents creep action. The centrifugal bolt of the delay mechanism moves outward com-pressing its spring. If the index plug is in the delay position, the copper plate is held by the plug and thus the central channel remains closed (Fig. 5). If the plug is in the instan-taneous position, the plate is moved by centrifugal force into the slot in the plug and the central channel is thus opened (Fig. 6).

On impact the needle is forced on to the detonator by direct action. On graze the de-tonator pellet is carried forward on to the needle. The flash from the detonator passes either through the delay channel or the central channel, according to the setting of the fuze, to the magazine and thence to the detonator and exploder in the shell.

Fig. 6

J.Gr.Z. 23 n.A. used with 75 mm separate ammunition and possibly 105 mm

The only difference between the above types is in the system controlling the delay.