"GRENADES 12.578). - The revival of the hand grenade in the Russo-Japanese War of 1904-5 resulted in new designs for weapons of this class being worked out in several countries, not only for hand grenades with a time fuze, but also for percussion grenades and for grenades fired from a rifle. In the World War the advent of trench warfare on the largest possible scale produced a sudden demand for grenades in enormous quantities and as pre-war and war-time designs were successively exposed to the test of active service conditions, while at the same time the needs of quantity production constantly imposed checks of another kind, grenade design passed through a rapid evolution from 1914 up to 1917 after which warfare became more open and the rifle and light machine-gun asserted themselves as the prime infantry weapons. It is proposed here to indicate the course of this evolution by describing representative patterns of grenade employed successively in the British and other armies.
During the course of the war, both hand and rifle grenades (especially the latter) were used as containers for gas and smoke compositions, as well as for illuminating and light-signalling purposes. These special grenades, as grenades, presented fewer problems of design than the explosive grenade, and the safety and ignition devices employed with them were simple adaptations of those used with the explosive grenade. They do not, therefore, require special treatment in the present connexion, and the following account will deal with the explosive grenade only.
Hand Grenades. - Perhaps the dominating characteristic of trench warfare as practised in 1914 and 1915 was the inability of the deeply entrenched infantry on each side to inflict damage upon the other otherwise than by high angle fire. Within the infantry arm itself, this high angle fire could at first be provided only by hand grenades. But as no one had foreseen the use of this weapon by infantry on a large scale, the available patterns in Great Britain and elsewhere (designed for use by skilled sappers in siege warfare) were of a somewhat complicated design. Thus, at the outbreak of the World War, the only grenade available in the British service was the" No. 1,"evolved after the Russo-Japanese War, and the only immediate means of supplementing it was a stock of" Hale's grenades which had been manufactured for the Mexican Government. These two, in very small quantities, formed the only armoury of the bomber in the early days of 1915, and soon the troops in the field began to improvise grenades out of jam tins and other receptacles, using any explosive and any form of igniter which was at hand. At the same time other types were worked out by the engineer branch of the War Office, and both then and afterwards countless inventors set to work to produce weapons of this class and submitted them to the military authorities, who sifted them, tested the more promising both on the experimental ground and in the trenches, and finally, where the advantages of a proposed new design outweighed the very serious drawbacks attendant upon manufacturing a new type and training the army to its use - considerations which ruled out many designs that were intrinsically very good - it was adopted as a service store. So far as concerns British grenades, only service stores will be dealt with in this article.
Thus, towards the end of 1915 or the spring of 1916 the types in use and in prospect were very numerous, and most of them were open to objections, either in point of safety to the user, or of trustworthiness in trench conditions, or of manufacture.
Considering them collectively, these grenades may be classified in two ways: according to their effect and according to their method of explosion. As regards the former, a distinction arose between those designed for concussion effect and those designed for fragmentation. From the same dual need of localized effect and of distributed effect which produced the two main classes of artillery shell, came "concussion" grenades which contained a maximum of explosive, contained in the thinnest possible case, and "fragmentation" grenades with heavy iron cases, provided only with the explosive necessary to impart wounding energy to the fragments, and having the iron prepared for the desired fragmentation by criss-cross weakening grooves. Each of these had the defects of its qualities; thus, the concussion grenade was only effective within a narrow radius from the point of burst, and the fragmentation grenade was liable when used in the open to kill the thrower himself with splinters coming back. Examples of each class will be found below, and it should be added that special grenades such as those used for smoke, for light and for gas, were in the intermediate position, having thin walls, so as to contain a maximum of composition and a small explosive charge sufficient merely to open the casing.
The second basis of classification, which from the designer's point of view was the more important, was the method of bursting the charge. In all grenades filled with H.E.' as in all shell so filled, a small charge of sensitive explosive is required to detonate the relatively inert main charge. This element is contained in a copper tube called a detonator and it is in the means of igniting this detonator and the safeties provided against its premature action that the whole art of grenade design resides. Many of the risks, indeed, only became evident as the result of active service experience - for instance, the risk that a man would be shot after putting the safety device out of action but before he could throw the grenade.
At the outset, the standard patterns of hand grenade had percussion ignition - that is, they were arranged to explode on contact 1 Certain German grenades were filled wholly or in part with black powder and needed no detonator.
with the ground or the target. Such grenades were "armed" and dangerous as they lay in the bomber's hand ready for throwing, since, whereas in an artillery shell or a rifle grenade the shock of discharge is available as a force for arming the ignition, in a hand grenade this has to be done by the bomber himself. They were, further, intrinsically more sensitive than artillery fuzes in that they had to act at very low striking velocities and even on soft ground. A very little experience of existing types, therefore, sufficed to turn the current of opinion in favour of time grenades, not because of any special utility and function such as those possessed by the time fuze of artillery but purely because a delay between ignition and explosion was the best practical form of safety. Five seconds was as a rule adopted as a standard interval, and this gave time in case of accident to throw the grenade to a safe distance, or to take cover or lie down. Later, in perfected designs, the percussion grenades came to the fore again, but only towards the end of the war, and these new types were never actually used by the British army in the field.
Apart from the question of safety, the percussion grenade - at least in all patterns previous to those embodying an all-ways fuze - had to be designed so as to fall on its nose. The usual method of ensuring this was by an air-drag in the form of streamers, attached to the tail or handle. Time grenades would of course act whatever the position in which they fell.
With percussion grenades the ignition device was simply armed by, or before, the act of throwing, but in all time grenades of course positive ignition was necessary. Many ignition devices were used and many others proposed; in general, they may be classified as friction lighters and striker-and-cap combinations. In either case, the actual ignition was done by the bomber. In many designs he ignited the grenade before throwing it. In some a cord, attached to his wrist and to the grenade, suddenly tightens when the grenade has travelled to the end of its tether (a few feet) and the parting jerk fires the ignition device. In others, which are the best known and most successful, ignition takes place automatically as (or shortly after) the grenade leaves his hand.
The charge employed in grenades naturally varies according to the intention of the design. In fragmentation grenades, as above mentioned, it is kept small (in the Mills grenade described below it is 21-3 oz. only, in a total weight of 1 lb. 8 oz.), whereas in concussion grenades - notably in the heavy tin-cased concussion grenades used in the earlier days of the war for wire cutting and demolition effect - it is at a maximum (3 lb. 9 oz. out of a total weight of 5 lb. in the Russian "obstacle" grenade). The permitted weights of hand grenades have also varied considerably. In 1915 heavy grenades intended to be thrown by trench engines (see Bomb Throwers) were in frequent use, but these were superseded by trench mortar bombs, just as their throwing engines were displaced by light trench mortars. The special grenades used with certain explosive-propellant throwers were also frequently of this heavy class. But for the hand grenade an upper limit was fixed when the ranges required on service and the throwing powers of the average bomber had been ascertained by experience. This limit was about 2 lb. in Germany and II lb. in Great Britain and France. To qualify as a bomber, a British soldier was required to pitch half of his (II lb.) bombs into a trench target measuring Io ft. longitudinally and 4 ft. laterally at a range of 30 yd., but specially expert men were capable of much longer throws. Another consideration limiting the size of hand grenades was that of ammunition supply in the very difficult conditions of trench fighting.
These two requirements, range and supply in the trenches, combined from 1916 onward to bring into use a much lighter form of grenade, colloquially called the "egg," which weighed only 11-12 oz. and could be thrown 50 yd. by an average bomber. At the same time the grenade of the I i lb. class began to be adapted for firing from a rifle, and thus to take the place of the rifle grenade, though it also remained in use as a hand grenade to the close of the war.
A representative percussison grenade of the earlier type is the British "No. 2" or Mexican Hale (figs. i and ia). Though light (i lb.) it is of the fragmenting class, for while the casing itself is thin, it is surrounded by a heavy iron collar prepared by grooves for fragmentation. The streamers and the presence of this collar well up on the head ensure a nose-first fall. In the interior is a central tube, the upper portion of which takes the detonator, the middle a creepspring and the lower a pellet with pointed striker. The pellet is held firmly by a safety-pin which is only Nvithdrawn at the last moment. When thrown, the parts retain their relative positions, but on impact inertia causes the striker pellet to fly forward, overcoming the creepspring, and its needle pierces the detonator and the grenade is exploded. It will be noted that, once the safety-pin is removed, the only safety device operating consists of a creepspring which is necessarily kept very weak.
An ingeniously designed French grenade which was much used in 1915, but later shared the fate of all percussion grenades, is shown in figs. 2 and 2a. It is pear-shaped and fragmenting but weighs hardly more than i lb. complete. Essentially its ignition arrangements consist in a lever with a weighted cord, a striker and a creepspring. Until the moment before throwing, the lever 7 is held in place by a string, which the bomber breaks with his left hand while firmly gripping the lever with his right. When the grenade is thrown, the lever flies up under the impulse of the spring 9 and the striker 5 is now held off the cap only by the creepspring 6. The lever 7 with the weighted cord it act as an air-drag to ensure nose-first impact. The head of the lever mo is pivoted eccentrically and its underside is formed to a curve which gives an initial leverage against the action of the spring 9, and therefore acts as a safety device.
'FIG.2 ' Cap Safety Pin Cap Detonator. FIG.3 The German "disc" percussion grenade (fig. 3) is designed so as to act in any position of fall. Ii has internally six radial channels, of which four are provided with striker pellets carrying caps, one contains the detonator, and the sixth has a safety pellet. In the centre is a fixed star, offering four striker points to the four striker pellets. These points are masked by arms or prongs on the safety pellet until the latter falls out of the grenade during flight and leaves them exposed. Then, whichever portion of the disc edge strikes the ground, the opposite striker pellet sets forward, dashing its cap on to the corresponding point of the star and so firing the detonator. A disc percussion grenade was also used with the Minucciani bombthrower described under Bombthrowers.
It will be noted that in both these cases the ignition arrangements constitute what is called in artillery language a "graze fuze," that is, the active element (the striker pellet) sets forward when the motion of the body of the grenade is checked on impact or graze. In other patterns, on the contrary, the ignition is of the "direct action" class, the pellet projecting from the head of the grenade Screwed Plug Safety Striker Pellet - Shell --- Ch arge 4 Pointed Star Brass Tub Detonator- Screwed Plug; and being forced back on to the detonator when the object is struck. To ensure this action, in the case of grenades, the outer end of the pellet is usually formed with a large disc or mushroom head which augments the surface of impact and therefore the resistance which tends to drive in the pellet.
A simple grenade of this kind is the "Japanese" grenade as employed by the Russian army in the World War (fig. 4). This is a heavy-bodied fragmentation grenade with a hood bound on by cord wrapping instead of streamers. It will be seen from the drawing that when the safety ring 6 is removed nothing holds the striker 5 away from the detonator cap except the tightness of fit of the striker rod in the india-rubber block 8. On impact the mushroom head 9 forces the striker in and the grenade is fired. This was a rather light grenade weighing about i lb. 4 oz. and ranged, in expert hands, to about 45 yards. It could not be used in the open, as fragments came back as far as 200 yards. It had no handle, being grasped by the body.
Time grenades, as already explained, possess the advantages of intrinsic safety and of being able to act in any position of fall, though in other respects inferior to percussion. The types described below have been selected (a) to show the variety of ignition devices employed and (b) to indicate the evolution of design generally during the war period.
The type of grenade shown in figs. 5 and 5a is a Russian pre-war design, based no doubt on Port Arthur experience. The model shown was brought out in 1914 to replace an earlier and heavier engine of similar design.
Between the detonator and the cap is a column of slow-burning composition 21 connected to the cap 19 by strands of quickmatch 25. As in almost all patterns of grenade, the detonator element is transported separately. In this case the parts which render the grenade "live" are assembled in a U-shaped body 18 which is dropped into position with the cap over the striker 6 and the detonator 22 in a cavity in the exploder 23, and clipped there by the fastener 20. The action is as follows: the bomber grips the handle, pressing on the lever 12, and thus by means of the sear a cocking the striker-spring 8 and striker 6. His fingers encircle the safetyring 15 (which has hitherto held the lever) in such a way that in throwing the grenade the ring will remain in his hand. He then withdraws the safety-pin 11 which limits the forward movement of the striker. When he throws the grenade, the spring 14 forces out the lever 12 and the striker 6, released from the sear a, flies forward under the influence of its spring and fires the cap. This, through a flash along the quickmatch 25, starts the slow-burning composition which in due course fires the detonator, exploder, and main charge. Though primarily a thin-walled "concussion" grenade, this pattern has the casing lined with metal rings 17 prepared for fragmenta tion.1 It will be noticed that the handle portion as well as the body proper is filled with explosive. Carrying nearly i lb. of H.E., this was a very formidable concussion grenade, serviceable and not too difficult to manufacture (in spite of its apparent complexity), and could safely be used in fighting in_the open.
In marked contrast to this grenade are the more or less improvised time grenades of 1915 of which the British "cricket ball," the French "Fi" and some German specimens may be taken as representatives. The British "cricket ball" (fig. 6) and its variant the "lemon" was a plain iron, spherical or ovoid shell into which was screwed a plate carrying a detonator sleeve. In preparing for action the detonator was placed in the sleeve and secured by wire. Crimped into the mouth of the detonator was a 5-seconds length of Bickford safety fuze, the other end of which was prepared with a patch of composition such as is used for safety matches. The protective cap 8 being pulled off, the grenade was ignited by rubbing the head against a strip of matchbox composition (tied on the bomber's sleeve), and thrown. The weight of this grenade in its cricket-ball form was 12 lb.
The French "defensive" (i.e. fragmenting) grenade "F1" weighed 1 lb. As shown in fig. 7 it was ignited by a blow. The cover io being removed, a sharp blow on the cardboard inner tube 4 (carrying the cap) forced the cap down on the striker, igniting the timefuze length 8.
The German 2-lb. ball grenade (fig. 8), unlike most, was powderfilled and, as it could therefore be fired by a flash, needed no sensi 1 The earlier (22-lb.) pattern had a large amount of "langridge" (i.e. small pieces of metal) packed round the explosive charge.
HG. 4 attached to the bomber's wrist, tightening when the bomb reached the end of its tether, jerked out this roughened bar and so effected ignition.
The German H.E. cylindrical grenade (fig. 9) had also a frictiontube igniter, but the bomber fired this by a pull on the attached wire before throwing. This was essentially a concussion or "offensive" grenade and remained in use throughout the war. It was provided with a handle and with a hook whereby to attach it to the waistbelt. In another type of cylindrical handled grenade, part of the H.E. charge was replaced by langridge 1 and the ignition was by a spring striker as in the "hairbrush" described below.
Another form of handled time grenade used by the Germans and then copied by the British was the "hairbrush." The German FIG 10a Section r --- ?.
' o -- ? o + d?
FIG. 10 pattern (figs. 10 and ioa) had a spring igniter of a simple character. In a tube (fig. ioa) inserted in the rear end of the detonator and time-fuze tube was a striker, striker spring and cap. A collar on the striker rod kept the spring in compression so long as the tail end of the rod was held by the safety-pin. As soon as this was withdrawn the spring reasserted itself and the striker flew forward, firing the cap and igniting the time fuze.
Neater in design, more trustworthy in action, and far more popular with the troops than other British types, the Mills grenade requires a more extended description (fig. II). If the number supplied, and the steadiness with which the type maintained its hold on opinion be a test, this grenade was the most important of all those used in the World War.
As its name implies, it was patented by Mr. William Mills, of Birmingham, but the idea was of Belgian origin; although it is fair to add that the original Belgian design differed very considerably from that which is now so familiar as the "Mills" grenade.
The No. 5 grenade, which was the first of several British service patterns of the Mills type, consisted of a barrel-shaped iron casting, fitted internally with an aluminium tube known as the "centre piece." Adjoining the centre tube, and communicating with it at the bottom end of the grenade was a cylindrical chamber for the reception of the detonator to which was attached a 5-second fuze, terminating in a rim-fire percussion cap, which was inserted in the end of the central tube. The lower end of the grenade was closed with a screwed plug, known as the "base plug," made in aluminium, 1 Some of the grenades improvised in the field by the British army were also partly filled with langridge or so-called "shrapnel." 2 tive detonator. Its ignition arrangement was somewhat similar to the familiar friction tube of artillery, viz. a roughened bar which was inserted in a tube coated with match composition. A cord ?, ?>
? ? screwed into base plug.
FIG. 11a EI v i brass, or a soft alloy, and which secured in position the detonating apparatus, and also formed a firm base to receive the shock of the striker when released from the lever. The high-explosive filling was introduced through an opening situated near the top of the grenade, closed with a brass screw, which, after filling, was carefully cemented into position. The cap was fired by means of a steel plunger, known as the "striker" which was operated by a powerful spring. The striker was held off the plug by means of an external lever provided close to one end, with small trunnions which rested in seatings formed on the head of the grenade. The shorter end of the lever was forked, the prongs of the fork engaging the projecting head of the striker. Thus, while the long end of the lever (which was bent to conform to the outer shape of the grenade) continued to be held in the thrower's hand or to be pinned down by the safety-pin the spring remained compressed and unable to drive the striker down on to the cap, but as soon as the lever was freed, the spring asserted itself, forcing the lever up (and out of its seatings) and the striker fired the cap. Modifications of the No. 5 were made later from time to time with the object of increasing its safety and efficiency, but its main features remained unaltered.
Originally the "Mills" grenade was intended purely and simply as a hand grenade, but it was found that its usefulness could be materially increased if means were adopted for projecting it from a rifle. This idea was considered and ultimately accomplished by substituting for the aluminium base plug one of steel, to the centre of which was attached a short steel rod 51 in. long. The rod, when inserted in the barrel of a rifle, enabled the grenade to be projected by the firing of a 35 gr. cordite blank cartridge, later replaced by the 43 gr. blank cartridge used for firing all rodded grenades.
In order to hold the lever in its correct position in relation to the grenade, and secure the striker until the moment of discharge from the rifle, a special appliance, known as a "rifle cup," was designed to fit on to the barrel of the rifle, and was secured to the barrel by the bayonet. The rifle cup consisted substantially of a flat steel ring slightly larger in diameter than the grenade, and projecting beyond the barrel of the rifle about 22 in., the ring being fixed concentrically with the rifle barrel. It will thus be seen that at whatever angle in relation to the horizontal plane, the grenade was inserted in the rifle cup, the lever was prevented from rising and thus releasing the striker until the grenade had been discharged, although the safety-pin had been previously withdrawn, leaving the lever otherwise free to act (fig. i ra).
This device had the effect of increasing the range of the grenade by about 50 yards. In this form the grenade was known by the description of "No. 23 Mark I" and perhaps attained its maximum of usefulness. Later developments of the Mills as a rifle grenade are dealt with below.
The "egg" class of hand grenades, alluded to earlier in this article, embody no novel technical devices and, therefore, need not be further described here. (C. F. A.) Rifle Grenades. - The desire to obtain increased range in a convenient way had already before the World War broke out led to the design of rifle grenades, which were, essentially, percussion grenades fitted with a steel tail-rod that was inserted in the bore of the service rifle and propelled by the force of a blank cartridge. In these rifle grenades, two forces became available to the designer which were not so in the case of hand grenades, viz. high velocity and therefore the possibility of causing and utilizing rotation, and the shock of discharge. Both these forces greatly facilitated the design of percussion grenades, as also did the fact that (given a suitable charge and conditions of firing) the tail rod ensured a nosefirst fall. The development of the rodded rifle grenade in the war period was therefore steadier and more consistent than that of hand grenades.
For most of the patterns used by the British army in the war, the original "No. 3" or "Hale's rifle grenade" (fig. 12) may be taken as representative in point of principle. It was a fragmentation grenade, as were all explosive rifle grenades, since the range eliminated danger from blowing back of fragments.
To the lower end of the body was fitted a base-piece of brass, which was bored out to receive a striker-rod and its needle. The outside of this base-piece was machined to receive a wind-vane, the boss of which held in position two safety bolts situated in the basepiece and preventing forward movement of the striker rod. Below the boss of the vane was a sleeve-like safety socket securing the boss above mentioned against premature rotation, so machined and slit that it clipped over the lower portion of the base-piece, this also being suitably machined. Into the lower end of the base-piece was screwed a steel rod, 10 in. long and of the calibre of the rifle, viz. .303 in. (In this and certain of the patterns which succeeded it a clip was fitted to the base-piece which was sprung over the muzzle of the rifle in order to secure the grenade in position.) The grenade body itself was traversed by a central tube, in the forward portion of which was secured the detonator in its sleeve, the middle portion containing a creepspring and the lower the point of the striker rod.
When the rifle was fired (a special 43 gr. blank cartridge was used) the safety socket set back, releasing the wind-vane which presently, under the action of the air, began to revolve and so to unscrew itself; in turn, this released the safety bolts which flew out, and thenceforward nothing but a light creepspring kept the detonator off the needle, which flew forward on graze and exploded the detonator and the bursting charge.
Steel Body ..Detonator 'FIG. 12 ' While the general principle of this grenade was maintained without change, certain defects of detail and other reasons for modification soon appeared. Thus, the difficulty of so much machining in a store which was required urgently and in enormous numbers, and the difficulty of keeping the wind-vane and its screw clean in trench conditions, led to the design of the vaneless "No. 20" in which the safety socket alone controlled the safety bolts, and considerations of manufacture, especially of filling conditions, led to further modifications in the types No. 24 and No. 35. These need not be dealt with in detail here. It should be mentioned, however, that the substitution of a service-rifle cartridge case (with its cap) for special detonator holders brought about a marked improvement in the direction of simplicity of manufacture.
Another British rifle grenade, known as the "Newton Pippin" or No. 22, was an improvised design by Capt. H. Newton, which was manufactured in the workshops of the army in the field. Its ignition arrangements were of the direct-action type, the mushroomheaded striker being forced back on impact. Other features of the grenade were the use of the service cartridge case as a detonator holder (a practice which, as has just been remarked, became general); the length of the rod (15 in.); and the provision of a gas-check on the end of the rod, a device used fairly frequently in other armies but not accepted in regulation British grenades. Ordinarily, the rod of the grenade does not seal the bore of the rifle, as it does not enter the grooves, and a proportion of the propellant force of the gas is therefore lost by escape round the rod. A gas-check, expanding into the grooves and then sealing them, obviates this, though of course the higher efficiency is obtained at the cost of an increased strain on the rifle.
Two other British types of rodded rifle grenade may be mentioned - the Sangster and the Steuart, distinguished by the numbers 25 and 39. In the former, which was of the direct-action class, a wind-vane attached to the striker screwed it down in flight until it left the screw thread and became sensitive. Owing to the careful design of the body and the use of a 15-in. rod, very long ranges were obtained with this grenade, but it was never adopted as a standard pattern owing to the same considerations of difficulty in manufacture and of service rough usage as those which had militated against earlier vaned patterns. The characteristic of the Steuart pattern was a safety device consisting in a sleeve which was slit across in manufacture so as to leave only a narrow web of metal; this sleeve was placed on the striker rod in such a way as to hold it firmly till the shock of discharge occurred, when the rod set back and a shearing blade fixed to it cut through the remaining metal of the sleeve. The striker rod was thus freed. The Steuart was a direct-action grenade. Experience had proved that, in spite of the relatively low velocity of rifle grenades, the conditions of grenade practice were similar to those of artillery in that graze fuzes, having a slight delay inherent in their design, were liable to act only after the projectile had more or less buried itself. It is preferable, therefore, that the ignition arrangements of a rifle - -- -Detonator Holder Fxplosive? Charge Firing Needle Brass Bose__ Piece II.
Safety Pin Base Plug.____ Sprin,Clip 10 Rod.-- - Detonator. Cap -Creep Spring -- -Neddie Pellet. --Retaining Bolts ---Wind Vane Releasing Socket 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 general arrangements are, as a rule, found, and a catalogue of the minor variations which are found would be of no interest to the non-technical 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 directaction and graze types are found, and a gas-check is almost invariably 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, Russian rifle grenades have the detonators (which are rather explodergaines than detonators in the British sense of the word) buried in the interior of the body. The usual length of rod was 152 in., which in a long rifle gives the same length of propellant chamber as a 10-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 container 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 container) projects into this central tube. The tendency of the spring therefore is to pull the cap on to the needle. The premature occurrence 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 consisting 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 surrounded 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 solidly fixed both during transport and when fired. Moreover, the spring in 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. Thereupon 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 velocity 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 discharger-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 protrude 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 rifle was attached, by a sleeve, the "tromblon" (an old word for blunderbuss) 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 rifle. 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 "mandrin") 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 ? ^I?
. ^I grenade was arranged for fragmentation and it had a direct-action ignition system. The maximum range was nearly 400 yards.
Expansion Chamber The German discharger-cup grenade, introduced in 1918 to replace rodded grenades, was in all but details a copy of the French V.B. It ranged to 150 metres. The ignition arrangement was simpler than in the French archetype.
The Russians also used a discharger-cup grenade in addition to their rodded rifle grenades. The grenade for this fuze had an adjustable time ring. (C. F. A.) The Grenade of the Future. - In Great Britain, a reconsideration of grenade problems in the middle of 1917 led to several modifications in the Mills grenade as such (the new pattern being designated No. 36) and in particular to the design of a discharger-cup for it. The rod was abandoned, and replaced by a steel disc 22 in. in diameter attached to the base plug. This fitted accurately into the cylindrical portion of the cup, and the whole of the escaping propellant gas was therefore usefully employed. This cup was used on active service in the last months of the war.
Meantime, research had again been directed to the percussion hand grenade. Various types had been tried but, owing chiefly to the fact that the Mills had become thoroughly familiar and was trusted by the army, none was actually adopted.
The fusion of hand and rifle grenades, however, was not imminent, and amongst the conditions laid down for the "grenade of the future" were that it was to be (I) a percussion grenade, but one that would act in any position of impact or fall without the necessity of any form of air-drag; (2) capable of use either as a hand grenade or as a rifle grenade; (3) safe (a) during the first To yd. of flight and (b) if dropped or accidentally knocked prior to throwing, but sensitive beyond ,o yd., even should it fall in soft mud; capable also of being picked up and thrown away when lying on the ground with all safeties removed; (4) weatherproof and mudproof; (5) simple to manufacture, to assemble in the field, and to use.
The last two conditions are obvious necessities in a service grenade required in vast quantities. The other three, however, involve technical questions of design and are largely interdependent. Thus, requirement (I) might be met by rotating the grenade by grooves in the discharger-cup and ridges on the grenade or vice versa (thus ensuring nose-first impact) were it not for requirement (2), and in requirement (3) the significance to the designer of the to-yd. frontier between "safe" and "sensitive" is different according as a hand-throw or an explosive propulsion is in prospect. A discussion of these requirements in detail, the technical elements available for meeting them, and the experimental patterns which have been evolved in accordance with this schedule of conditions lies outside the scope of this article. It must suffice to say that the problem thus set is one of great difficulty, but that, with the harvest of experience gained in grenade design during the war period, it is by no means insoluble. One or two questions of a general character should, however, be mentioned in conclusion.
The range and weight of the grenade of the future will depend undoubtedly on the final interpretation of the lessons of the war. The tendency to increase range will be checked at some upper limit fixed by the capacity of the infantr y man's standard weapon to endure the strain. Beyond that limit a special weapon will be required, and this will either compete with or fuze with the light trench mortar, but in either case its projectile will cease to be a grenade in the ordinary acceptation of the term. On the other hand the lower limit of weight of projectile remains fixed by the necessity of producing adequate effect on explosion. Under existing conditions it may be stated, as a rough indication, that the lower limit of weight compatible with effect is hardly, if at all, below i lb., and that 300-350 yd. represents the upper limit of weight for 1 - 12lb. bombs fired from a discharger-cup fitted to the ordinary rifle.
Another question of importance is the means used for varying the range. As a hand-thrown weapon of course the grenade is brought on to its target by the skilled eye and hand of the thrower, but as a rifle grenade it requires mechanical adjustment. During the war, special rifle-grenade stands were designed, into which the rifle was clamped, but such devices may be considered as proper to trench warfare only, and the problem of the present day is to find a means of varying the trajectory of the grenade which is adaptable to the individual rifle. Two solutions have offered themselves. One is varying the pressure of the propellant gas by varying the position of the grenade in the cup, as in the French D.R. grenade and mandrill, the discharger-cup used in the last months of the war for the Mills grenade, and other types. Opinion is divided on the merits of this method, which, though attractive in other respects, is open to criticism because it does not legislate for wind - a specially important factor in shooting with a large object of low velocity such as the grenade, and also because such an adjustment may easily be forgotten or mis-set in battle conditions. The alternative is to provide a simple form of clinometer or elevation indicator on the rifle. (C. E. W. B.)
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