This base fuze is of the graze type and used in German 3.7 cm A.P. shell of Polish origin. A drawing showering its external contour and markings is included in Fig. 7.

The fuze consists principally of a steel body, steel inertia-pellet containing detonating composition, brass ferrule, two steel balls, brass arming sleeve, a small and a large stir-rup spring, and a felt disc.

The body is in two parts. The rear part is flanged, and screwthreaded externally for in-sertion in the shell. Internally it is screwthreaded to receive the front portion, and bored in two diameters to accommodate the fuze mechanism. The front part is screwthreaded externally at one end for attachment to the rear part, and is tapered to the front to a tubular closed end. The tapered portion is bored radially to form two rows of three holes each. An internal needle of formed in the closed end and is intergral with the body.

The inertia pellet is cylindrical with a solid closed base end. Externally, near the base, it is recessed circumferentially, and above the recess are two indents, diametrically oppo-sed, which partly accommodate the two balls.

The pellet contains 0.89 grains of C.E. and a capsule of detonating composition. The copper capsule is cup-shaped with a hole in its base which is closed on its inside by a copper disc 0.033 inches thick. Above the disc is a composition, weighing 0.026 grams, and consisting of mercury fulminate 22.0 per cent. potassium chlorate, 40.5 per cent. antimony sulphide 33.6 per cent. and ground glass 3.9 per cent. Above this composition is a pellet of mercury fulminate weighing 0.57 grams with a thin layer of T.N.T. weighing 0.04 grams on top. The capsule is inserted in the inertia pellet open end first, and se-cond by turning the end of the pellet over the base of the capsule and varnished the join.

A felt disc is inserted between the base of the inertia pellet and the fuze body.

The ferrule is cylindrical with an external circumferential recess about is centre.

Near its forward end are two holes, bored diametrically opposite, which partly accommo-date the two steel balls. The ferrule surrounds the base end of the inertia pellet and is supported by the smaller of the two stirrup springs.

The stirrup spring is cylindrical, its lower edge has three external projections which fit under the ferrule and its upper edge has three internal projections which engage in the recess near the base of the inertia pellet.

The arming sleeve is cylindrical with a circumferential internal recess near its base edge. It surrounds the forward part of the ferrule and retains the two steel balls locking the inertia pellet in the safe position. The sleeve is supported by the larger stirrup spring.

The stirrup spring is cylindrical and split. Two lugs, cut diametrically opposite in its lower edge. project and fit under the arming sleeve.

Before firing. – The inertia pellet is locked and held away from the needle by the two steel balls which are retained by the arming sleeve.

After firing. – On acceleration, the arming sleeve sets back and is retained by the larger stirrup spring which engages the circumferential groove, thereby freeing the two balls which move outwards under centrifugal action. Creep action is prevented by the smaller of the two stirrup springs.

On impact or graze the inertia pellet moves forward on to the needle and detonates its filling.

Fig. 7