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 care- Fully cemented into position. The cap was fired by means of a steel plunger, known as the " striker " which was operated by a pow- erful 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 5j 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 2j 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 gren- ade 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. lia).
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 maxi- mum of usefulness. Later developments of the Mills as a rifle gren- ade 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 con- venient way had already before the World War broke out led to the design of rifle grenades, which were, essentially, percussion gren- ades 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 nose- first 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 " Kale's rifle grenade " (fig. 12) may be taken as representative in point of principle. It was a fragmenta- tion 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 out- side of this base-piece was machined to receive a wind-vane, the boss of which held in position two safety bolts situated in the base- piece 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.
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Neddie Pel/er \ . -Retaining Bolts
Wind Vont
He/easing Socket
10 Rod
FIG. 12
While the general principle of this grenade was maintained with- out change, certain defects of detail and other reasons for modifi- cation 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 con- siderations 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 mushroom- headed 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, expand- ing 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 men- tioned the Sangster and the Steuart, distinguished by the num- bers 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 l^-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 mili- tated 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 roof 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
