The fuze is used in the Q.F. 102 mm 35 calibre anti-aircraft gun ammunition and is a ten-sioned fuze of the combustion type. The setting graduations extend from zero to 13.2. A fuze set to 13 grave a time of burning of 26.6 secs. ar rest. The design includes a delay arrangement between the lower time ring and the magazine which ensures a minimum time of burning of 0.6 sec., and thus provides for safety against a "flash-over" in the bore of the results of a dangerously short setting. The screw-threaded protion of the fuze for insertion in the shell is 1.762 inches in diameter.

The exterior of the fuze, visible when assembled in the shell, is of aluminium or aluminium alloy. The tension cap and the upper ring are shaped to coincide and form an ogival head. The lower ring is cylindrical and the flange of the platform is tapered. The setting graduations may be marked on the lower ring or on the flange of the graduations may be marked on the lower ring or on the flange of the platform. A soldered alloy cover with tear-off wire and ring is sometimes fitted to the fuze. The cover is marked with a red arrow and the word "TIRARE", indicating the method of removal.

The aluminium body of the fuze is screw-threaded to a depth of 0.4 inch for insertion in the shell and is shaped to form a platform to support the lower time ring. The tapered flange of the platform may be grooved to receive the soldered alloy cover and the tear-off wire, or may be graduated for the setting of the lower time ring. The numbered gra-duation extend from 0 to 13. These are subdivi-ded in tenths except between 0 and 1, where the subdivision commences at 0.8. The space between 0 and this graduation is barred out by two crossed diagonal lines. The subdivision continues beyond the 13 gra-duation to 13.2. A circular recess in the platform communicates with an inclined flash channel leading to the magazine. The recess contains an aluminium disc, with a central hole tapering towards the top, which contains a pressed filling of powder and introduces a 0.3 sec. delay. A felt washer, with a hole to correspond with the position of the delay unit, is attached to the platform by an adhesive. The inclined flash channel contains a solid pellet of powder, which gives a further delay of 0.3 sec. The magazine contains a 24-grain filling of granular gun-powder and is closed by an aluminium base piece which screws into the body with a left-hand thread and protrudes at the base. The base piece has a central flash channel, which is slightly closed at its inner end by a thin disc of alu-minium. The body is cylindrical above the platform for the assembly of the two time rings, and is screw-threaded to receive the tensioning cap. Two semi-circular recesses are formed in the cylindrical part of the body which coincide with similar recesses in the up-per time ring to receive the two aluminium locking pins which hold the upper time ring in a fixed position. A recess formed in the front end of the body contains the detonator as-sembly. A steel needle is fixed in the base of the recess, and a flash channel is drilled through the wall coincide with a similar channel in the upper time ring.

The detonator assembly consists of an igniferous detonator carried in a cylindrical alumi-nium pellet which is held off the needle by a slotted brass sleeve. The detonator is retai-ned in the pellet by a brass screwed plug. The slotted brass sleeve supporting the pellet is a tight fit round the base of the pellet, and is itself supported by a shoulder formed in the recess. Movement of the sleeve is prevented by a brass locking pin which is inserted through the wall of the recess and engages in the slot.

The lower time ring is of aluminium and is the setting ring. The groove containing the fuze powder in its underside extends through 310 degrees and has two circular vents for the escape of pressure and a flash-hole leading to the upper surface of the ring. The first vent and the flash-hole are connected with the commencement of the powder groo-ve. The second vent is similar and is located at 150 degrees from the commmencement of the powder groove. The first vent contains a pressing of powder, and both vents are closed by tin discs, which are secured by stabbing and sealed with varnish. The flash-hole connecting the commencement of the powder groove with the upper surface of the ring contains a filling pressed powder. A hole is drilled through this pressing and the pow-der in the groove beneath it to assist ignition. A washer of vegetable paper, with a hole to correspond with the commencement of the groove, is fixed to the underside of the ring to cover the powder groove, and a felt washer, perforated to correspond with the flash-hole, is fixed to the upper surface. A recess is formed in the cylindrical exterior wall of the ring for the setting key.

The fixed upper time ring is also of aluminium with a powder groove in its underside, which also extends through 310 degrees. Two vents are provided for the escape of pres-sure. The first is of the elongated type, and is formed in the bridge, or solid portion of the ring between the ends of the powder groove, and is connected to the commence-ment of the groove by a circular hole. This vent contains no filling, and is closed by a tin disc. The second vent is circular and smaller, and is located at 150 degrees from the commencement of the powder groove. A small hole through the powder filling is continu-ed slightly into the fuze powder in the groove. The vent is closed by two tin discs. In both vents the closing discs are secured by stabbing and sealed with varnish. An inclined flash-hole is formed in the inner wall of the ring at the commencement of the powder groove. The powder filling in the flash-hole has a central perforation, which corresponds with a similar vertical perforation in the fuze powder at 0.1 inch from the commencement of the groove. The flash-hole in the ring is held coincident with the flash-hole in the body by the two locking pins. A washer of vegetable paper is fixed to the underside of the ring to cover the powder groove. A hole in the washer corresponds with the com-mencement of the groove.

The aluminium tension cap is screwed over the forward end of the body to obtain the re-quired resistance to the turning of the lower ring, and is secured by a brass grub screw.

8.4 per cent

9.5 per cent

73.2 per cent

75.5 per cent

14.7 per cent

14.6 per cent

3.7 per cent

0.4 per cent

On acceleration the detonator pellet sets back through the slotted sleeve and the deto-nator is impinged on the needle. The flash produced passes through the flash channel in the recess and ignites the powder in the flash channel in the upper ring, thus igniting the fuze powder, which commences to burn along the groove in the underside of the ring. The pressure set up by the burning fuze powder dislodges the closing disc of the first vent, and thus prevents variation in the rate of burning as the result of heat and pres-sure. The distance between the commencement of the powder groove in the upper ring and the powder-filled flash-hole in the surface of the lower ring depends upon the angle through which the lower ring is turned in setting. When the fuze powder in the upper ring has burned round to this surface flash-hole the fuze powder in the lower ring is ignited through the powder in the flash-hole. The closing disc of the vent is blown out and the fuze powder burns round the groove to the delay unit in the platform. From the delay unit the flash is passed to the solid powder pellet in the flash channel, and thence to the magazine.

The second vent in each of the rings is blown open when the fuze powder has burned round to the position of the vent.

With the lower ring set to the zero graduation the flash-hole in its surface is aligned with commencement of the powder groove in the upper ring and the delay unit in the plat-form. Thus the flash from the detonator is transmitted directly to the delay unit.

With the lower ring set to the cross which indicates the safe position, the surface flash-hole in the lower ring is masked by the solid portion between the ends of the groove in the upper ring. Also, the delay unit in the platform is masked by the corresponding por-tion of the lower ring.