The fuze is of the igniferous type and is used with a gaine in the anti-concrete shell (Gr. 19 Be) for the 15 cm medium howitzer (s.F.H. 18). The shell is described in Pamphlet No. 8. The designation of the fuze "Bd.Z. f. 15 cm Gr. 19 Be.", is stamped in the base which carries a flat ring graduated to indicate the setting positions for non delay (OV), short delay (KV), and long delay (GV). The setting plug, in the centre of the ring, has a slot for the setting key and a setting index in the form of a line at right angles to the slot.

The graze mechanism is assembled in a cylindrical container, capable of rotation within the fuze body, and consists of a fixed needle and an inertia pellet carrying an igniferous detonator. The pellet is held away from the needle by five pivoted centrifugal segments mounted on a ring shaped holder and encircled by an expanding spring ring. There is no creep spring.

The cylindrical container of the mechanism is retained in the body by a screwed securing ring engaging a shoulder near the base and has a diametrical projection at the base to engage a corresponding slot in the front face of the setting plug. The top of the contai-ner is closed by the needle holder which is secured by four screws and has an inclined flash channel.

The setting plug, slotted to engage the container, is coned to correspond with a coned seating in the body and is secured by a screwed ring. A sealing washer of lead is held between circular grooves in the plug and the ring. The key slot in the base of the plug is at right angles to the container slot but for clarity is shown parallel in the drawing.

A diaphragm formed in the body of the fuze separates the large recess for the mecha-nism container from the small recess at the head for the delay unit and the magazine. The diaphragm has three equally spaced flash holes, with any one of which the inclined flash channel in the needle holder can be aligned by rotating the setting plug to the ap-propriate graduation on the setting ring. Felt discs and an aluminium disc with perfora-tions corresponding with the flash holes are inserted between the needle holder and the underside of the diaphragm. A recess for the locating pin of the delay unit is formed in the top of the diaphragm which is covered by similar felt discs.

The delay unit is held fixed in its recess by a locating pin in its base and consists of a cylindrical aluminium pellet with three equally spaced longitudinal channels of about 0.1 inch diameter which coincide with the flash holes in the diaphragm. One of these chan-nels contains no filling and provides a direct flash channel leading to the magazine when the inclined channel in the needle holder is aligned with it by rotating the setting plug to the "OV" graduation. The two other channels contain a pressed filling of delay composi-tion with a central cavity of about 0.04 inch diameter formed from the top. The cavity assists in the ignition of the gunpowder in the magazine, the depth being designed to give the required effective thickness in the delay composition (i.e., about 0.2 inch in the long delay channel and 0.15 inch in the short).

The magazine consists of a screwed plug recesses at the underside to contain the gun-powder filling. A flash hole formed in the centre is closed on the inside by a paper disc.

Fig. 6

Before loading, the fuze is set for non-delay, short delay or long delay by turning the setting plug so that the index line on the plug coincides with the "OV", "KV", or "GV" gra-duations respectively. The turning movement of the plug is imparted to the mechansim container tube bringing the inclined channel in the needle holder into alignment with the appropriate hole in the diaphragm and channel in the delay unit.

During the travel of the shell up the bore, the pressure of the propellant gases pressed the coned setting plug into its coned seating and compresses the lead washer between the plug and its securing ring. The gases are thus prevented from entering the fuze.

During flight, the coil of the expanding spring ring is enlarged and the segments swung clear of the path of the graze pellet by centrifugal force. Independent roatation of the mechanism container is prevented by the setting plug forced tightly into its seating

On graze, the pellet moves forward and the detonator is pierced by the needle. The flash from the detonator passes through the inclined channel in the needle holder and enters the hole in the diaphragm with which this channel has been aligned by the setting. With the fuze set for non-delay, the inclined channel is aligned with the hole corresponding with the empty channel in the delay unit, so the flash passes direct to the powder in the magazine. When set for short or long delay, the inclined channel coincides with the holes in the diaphragm corresponding with the appropriate channel in the delay unit. The flash then ignites the delay composition in the channel which burns through to the magazine.

With the setting plug at any position other than those indicated on the graduated ring, the inclined channel in the needle holder is masked by the washers and the solid parts of diaphragm. This would most probably prevent the ignition of the magazine and result in a "blind".