grenade should resemble in principle the artillery " instantaneous " fuze so as to ensure a burst above ground.
In the rodded rifle grenades used by foreign armies, the same gen- eral arrangements are, as a rule, found, and a catalogue of the minor variations which are found would be of no interest to the non-techni- cal reader. As France (and America) did not employ rodded rifle grenades at all in the World War, interest centres practically on German and Russian designs. These are not numerous. Both direct- action and graze types are found, and a gas-check is almost invari- ably fitted to the rod. A tin saucer is sometimes fitted to graze types to prevent the grenade from burying itself in soft ground. Both German types, model 1913 and model 1914, are complicated, especially the latter, which is organized with all the elaboration characteristic of German artillery fuzes of the period. Russian types are usually simpler, and reflect the lessons of active service experience in demanding little or no expertness in the user. Whereas elsewhere it is the almost invariable practice to keep the detonator element separate in transport, and to assemble it in the field, Rus- sian rifle grenades have the detonators (which are rather exploder- gaines than detonators in the British sense of the word) buried in the interior of the body. The usual length of rod was 15^ in., which in a long rifle gives the same length of propellant chamber as a lo-in. rod in the short rifle.
One Russian type, however, merits a 'full description as it has several unique features. This is the Mgebrov, illustrated in fig. 13.
Against its complexity and evident difficulty of manufacture must
be set the positive and " fool-proof " character of its safeties which
are such that the bomber is not even called upon to withdraw a
safety-pin.
The outer casing I is thick (for fragmentation) and inside this outer casing is a separate thin-walled explosive container 2 which is capable of a slight forward movement. The bottom of this con- tainer is formed with an incurving lip 14, and it is traversed from end to end by a central tube 13, longer than itself. In this central tube are an extended spring and the pellet containing cap and detonator 12, 15, 17. The spring is attached to the top socket of the tube and to the cap-holder of the pellet. The striker-rod with its needle 16 (which is fixed to the outer shell and not to the con- tainer) projects into this central tube. The tendency of the spring therefore is to pull the cap on to the needle. The premature occur- rence of this is prevented by two sets of safety devices in which reside, as usual, the ingenuity and the complication of the design.
Under the base of the detonator pellet is formed a detent a con- sisting of a short stem with a barbed end. This end is buried in a block of fusible alloy, which is itself in a cup that is nearly sur- rounded by thermit 18. The thermit chamber has holes to provide air for combustion and communicates by a channel with the hollow tail-rod 3, which is filled with powder composition 19. All these elements are rigidly attached to the outer case and tail-rod and the detonator pellet is therefore solidlj^ fixed both during transport and when fired. Moreover, the spring m the central tube tends to bind the unattached explosive container to its supporting platform 6, thus avoiding any shock due to set-back on discharge.
On firing, the flash ignites the powder in the tail-rod which burns through to the thermit chamber and ignites the thermit. This instantly develops so high a temperature that the fusible alloy in its cup melts away, freeing the barb of the detent a and therefore the detonator pellet. This takes place after four seconds, and the detonator pellet is now gently pulled forward by the spring. There- upon the second set of safeties comes into play. This consists in two
pivoted catches 7, the lower ends of which bear (through slots in the central tube) on the sides of the detonator pellet, and are held there by small springs 8. The pivots of these catches lie in the rigid platform 6 which supports the explosive container, and their upper ends engage in the annular lip 14 formed on its underside.
On graze, the explosive container sets forward, and its under-lip actuates the two catches so that their lower ends no longer bite on the detonator pellet ; this latter is then quite free and, under the combined influence of inertia and of its contracting spring, moves violently forward in the central tube, dashes its cap on to the needle and explodes the grenade.
To complete this survey of rodded rifle grenades it remains to mention the British Nos. 44 and 45 anti-tank grenades. These, having often to be fired almost at point blank, had short rods (8 in.) and a calico vane to ensure front contact. Unlike all the types above described, they were designed purely for concussion, having tin bodies and a maximum explosive content. The ignition was of the graze-fuze type. These engines gave a very efficient shattering effect on the hard steel of British tanks and seriously bulged the mild steel of German tanks, besides producing marked shock effects.
(C. E. W. B.; C. F. A.)
Discharger-Cup Grenades. It has already been mentioned that the French army never adopted the rodded rifle grenade. The objections to the rod are indeed serious, quite apart from the fact that it is awkward to handle and requires careful treatment. The rifle tends to bulge and eventually to split in the barrel, especially with the shorter rods, since the propellant gases impinge upon the end of the rod at high velocity and set up wave pressure at the point of contact. This is true, however accurately straight the rods may be. If they are not so, they buckle in the bore and the barrel bursts, probably with fatal results to the firer; in this case it is obviously the longer rod which is the more dangerous. Further, the general strain of firing rodded grenades shakes the rifle to pieces after some time, especially with long-rodded grenades in which heavy recoil is accepted for the sake of obtaining high muzzle velo- city and ranging power.
In the latter part of the World War, therefore, we find a general tendency to discard rodded grenades in favour of the discharger-cup or tromblon. In Great Britain this tendency began to show itself after the fitting of the muzzle attachment above described for the Mills grenade. This was not a true discharger-cup since the grenade was rodded and the cup was merely intended to hold down the Mills lever before firing, but its success established the principle that hand and rifle grenades should be as nearly as possible interchangeable, and this requirement was bound in the long run to lead to the dis- charger-cup in some form.
The pioneers in developing the discharger-cup were the French,
whose Viven-Bessieres or " V.B." grenade (fig. 14) became as
famous in war as the Mills hand grenade. This was a cylindrical
fragmentation grenade with a hollow passage through its middle.
The ignition arrangement was peculiar. The detonator and time
composition were mounted in a tube parallel and adjacent to the
central passage, and at the head of this tube, at right angles to
its axis, was a small cap-cartridge. A flat spring called the palette,
carrying a pointed striker, was mounted in such a way as to pro-
trude into the central passage. The space in the grenade cylinder
not taken up by the central passage and the detonator and fuze
tube was of course filled with explosive. To the muzzle of the rille
was attached, by a sleeve, the " tromblon " (an old word for blun-
derbuss) or discharger-cup which was cylindrical for the greater
part of its length and coned for the rest. When the grenade was
placed in this, the axis of the central passage was in line with the
axis of the bore of the rille. An ordinary bulleted service cartridge
was employed.
When the rifle was fired, the bullet, on leaving the muzzle, passed through the central passage of the grenade giving a sharp inward blow to the palette and thus firing the cap. At the same time the expanding gases from the bore filled the conical space in the cup and propelled the grenade.
This combination of cup and grenade proved very serviceable, its chief defect being shortness of range (180 metres) as compared with the rodded grenade. For longer ranges a different discharger was employed known as the D.R. In this, the cup (called a " man- drin ") was externally cylindrical and internally coned (fig. 15), and the grenade had a sleeve with external vanes (cf. the grenades of the German Granatwerfer described under BOMBTHROWERS. A blank cartridge was employed. The sleeve of the grenade was slid over the outside of the cup as far down as the regulating pin allowed it to go, the function of this pin being to regulate the volume of the gas expansion chamber and therefore the range. The body of the
