This is an igniferous base fuze of the graze type with delay action and is used in shell for heavy guns, the ammunition of which is often of naval design.

The body is of steel, brass plated, and closed at the forward end by a screwed-in brass head with a central cavity and flash hole sealed with a brass disc and varnish. The body is screwthreaded externally for insertion into the shell and recessed internally to take the graze mechanism. The head is screwthreaded internally to take a brass plug which holds a screwed brass delay unit at its forward end.

The needle is of steel and is secured by a steel plug which screws into the needle holder. The point of the needle protrudes into the top of the graze pellet. The recess in the fuze body houses a steel platform which carries five centrifugal segments overlapping the top of the brass graze pellet. The segments are encircled by an expanding ring of phosphor bronze which retains them in the overlapping position and thus prevents forward move-ment of the graze pellet.

The brass pellet, which is closed at the base by a screwed-in steel plug, houses a deto-nator holder resting on a fibre washer. The detonator consists of a copper shell closed at the top by copper disc and at the bottom by a copper disc with a square hole in the centre covered by a paper disc. The filling consists of 1.2 grains of detonating composi-tion over 13 grains of gunpowder. The composition is made up of mercury fulminate 21.3 per cent., potassium chlorate 44.0 per cent., antimony sulphide 34.0 per cent., and grit 0.7 per cent.

The delay unit is in the form of a brass plug with a central flash hole in the base and a recess filled with 0.8 grains of pressed gunpowder. An eccentric flash hole leads to a lar-ger recess in the forward end of the unit which contains 1.2 grains of pressed gunpow-der. Above the delay unit is a filling of 23 grains of pressed gunpowder contained in a re-cess in the brass head of the fuze.

Centrifugal force set up by the spin of the projectile in flight causes the spring ring to expand and permit the segments to rotate on their pivots thus freeing the graze pellet which, as there is no creep spring, tends to creep forwards towards the needle. The de-tonator is pierced immediately on graze or impact and the flash produced passes through the flash holes in the needle holder to the delay unit.

Fig. 6