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centrifugal action, the leaves of the shutter, one by one, rotate clear of the head of the inertia pellet. This is of a peculiar design, only found in German fuzes. On two sides the mass of the pellet is con- tinued upwards to form walls or guides, and between these guides is the needle, mounted on a fixed bar. In the upward motion of the pellet, therefore, the detonator carried with it is impelled straight on to the needle. A further peculiarity is to be noticed in the top part of the fuze. This is a delay-action fuze, and in order to damp the violence of the detonator its flash is compelled to follow a long and tortuous channel before it can reach the loose powder which ignites the delay pellet.

German percussion fuzes with optional delay are generally very elaborate; examples, however, may be given of the simple types.

In the 1916 Howitzer Fuze (H.Z. 16) shown in fig. 16 the usual

Centrifugal Bolt Detonator

Needle

Picric Acid

Delay Channel

elements a fixed needle and a movable pellet held by centrifugal bolts, a creep-spring and a shutter containing a relay pellet appear, and need not be further explained. The peculiarity of the fuze lies in the fact that between the detonator and this relay pellet the flash has two alternative paths, one direct and the other through a delay composition arrangement, either of which can be put into action in the setting of the fuze. Below the fire-hole into which the flash of the first detonator passes are two channels, into both of which it goes. But if the direct channel is blocked by the screw-in valve, the only passage is through the combination of powder, delay composition, and perforated powder pellet in the delay channel; this gives the required delay. In either case a relay detonator below the junction of the alternative channels passes on the ignition to the patch in the shutter and so to the gaine. The blocking or opening of the direct channel is effected, as the drawing shows, by screwing a simple screw valve home or out.

SECTION C. C. NOTE In all Sections the Fuze is set to Delay

PART SECTION A. A.

Centril Delay

PART SECTION B. B.

FIG. 17.

INVERTED PLAN

Shewing positions of the three) systems and the Main Detonator

The next example is more complicated, and introduces the device, already alluded to, of powder safeties. It is called " 1904 Shell Fuze without Striker Rod " (Gr. Z.O4 ohne Vorstecker), to distinguish it from the same fuze with a long striker rod used with a false-cap shell (fig. 17).

Above the main detonator is a powder arrangement consisting partly of loose powder and partly of delay powder, with two per- cussion systems of the guide and bar-needle type above described. A hole from the pellet on one side (section A-A) leads to the central delay, while a similar hole from the other pellet (section B-B) leads to the loose powder under the delay, thus giving delay or direct action as required. The two pellets are held away from the bar- needles by brass plungers with springs pressing on the closed-up tops of the pellet extensions, these plungers being themselves held in position by short columns of pressed powder. From these pieces of pressed powder, columns of powder lead to a platform at the upper

part of the fuze body. Here is a movable ring with an annular powder channel on its under side that ignites at will both or only one of the powder columns, in much the same way as the corresponding element of a time fuze. In the upper part of the fuze, placed centrally, is the ignition device. In the lower part of the fuze and in the gaine, also centrally placed, are the main detonator and the gaine elements to be described presently. Through the body of the fuze run three parallel and distinct systems, each of which is seen in one of the three sections shown in fig. 17. Each of these systems communicates with the igni- tion device in the head, and with the main detonator and gaine below, in a different way.

Centrally in the head of the fuze is the ignition device, analogous to that of a time fuze and consisting of a detonator pellet controlled by a compressed spiral spring cap, and held away from the needle below it by a split brass sleeve. A flash-hole leads from this pellet to the powder channel in the movable ring, and a second flash-hole leads to the third of the internal systems, a powder column passing down the body of the fuze body (see section C-C). This column joins another of rather larger diameter which consists of compressed powder, and acts as a stop to a brass retaining rod. The rod holds down an annular or tubular container situated in the gaine which is centred on a fixed guide rod and has beneath it a compressed spiral spring, to impel it forward when the retaining rod above it is liber- ated by the burning of the powder safety.

Upon shock of discharge the ignition pellet at the top of the fuze, overcoming the resistance of the split sleeve, sets back on to the needle and fires, the flash passing both to the powder in the movable ring and to the powder column which retains the brass rod (section C-C). When the movable ring is set for non-delay action, the flame passes from the powder in the ring to both the powder columns in sections A-A and B-B, but if set for delay it passes only to the column leading to the delay powder (section A-A). When the compressed powder in the columns is consumed and the plungers are freed, the detonator pellets (or, in the case of delay, that in section A-A) can move forward on impact and will be fired by the needles. Mean- while, in either case the column of powder in section C-C is consumed, the retaining rod is free to move, and the brass container moves for- ward under the action of its spring and fits over the main detonator. On impact, if the ring has been set for delay, one percussion detona- tor (that in section A-A) fires and ignites the central delay, which then burns through and ignites the loose powder below; and so in sequence are fired the main detonator, the container fitting round it, and the gaine. If the ring be set for non-delay, both percussion detonators (A-A, B-B) fire, but as one (section B-B) is in direct com- munication with the powder below the delay, the main detonator will be fired without any pause; in other words, the fuze behaves as one constructed for direct action on impact.

An objection common to all forms of powder safety is the risk of the powder becoming damp in storage or transport; if the safeties fail to ignite, the fuze will fail to act.

No attempt need be made here to describe trench-mortar fuzes; these are in the main impact or delay fuzes of a simple type designed to arm at low velocities. Practically all German trench mortars were rifled, and of the rest the most important types had either a stick or vanes to keep the shell-nose first in descent, so that the difficulty which in England led to the production of the " All-ways " fuze scarcely existed for them. One curious development should, how- ever, be noted a chemical fuze giving I, 2, 24 or 48 hours' delay according to the strength of the chemical used. 'In this, the needle was held off the detonator, against the effort of a spring to decompress itself, by a wire which passed through a container full of corrosive liquid and was secured beyond it to a convenient point on or in the

crew Plug

reeping Spring .Striker Ferrule

Detonator Powder Pellet 'etonator Holder Powder ^Stirrup Spring

Wax Disc

FIG. 1 8.

body of the fuze. Kept in tension by the effort of the spring, the wire was gradually eaten through by the corrosive liquid, and finally