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 pos- sessed 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 ensur- ing 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 2j3 oz. only, in a total weight of I Ib. 8 oz.), whereas in concus- sion 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 Ib. 9 oz. out of a total weight of 5 Ib. 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 dis- placed 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 Ib. in Germany and l| Ib. in Great Britain and France. To qualify as a bomber, a British soldier was required to pitch half of his (\\ Ib.) bombs into a trench target measuring 10 ft. longitudinally and 4 ft. laterally at a range of 30 yd., but specially expert men were capable of much lonrer throws. Another considera- tion limiting the size of hand rrenades was that of ammunition sup- ply in the very difficult conditions of trench fighting.
These two requirements, range and supply in the trenches, com- bined from 1916 onward to bring into use a much lighter form of grenade, colloquially called the "egg," which weighed only 1112 oz. and could be thrown 50 yd. by an average bomber. At the same time the grenade of the 1 1 Ib. 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.
Safety Pin (
Creep Spring
FIG. la
A representative percussison grenade of the earlier type is the British " No. 2 " or Mexican Hale (figs. I and la). Though light (i Ib.) 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 withdrawn
at the last moment. When thrown, the parts retain their relative
positions, but on impact inertia causes the striker pellet to fly for-
ward, overcoming the creepspring, and its needle pierces the detona-
tor 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 Ib. complete. Essentially its igni- tion 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 1 1 act as an air-drag to en- sure nose-first impact. The head of the lever 10 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
"'/^....Safety Pi"
_ Safety PeH<*
.. Striker Pellet .Shell
- Charge 4 Pointed Star
BrassTub
Detonator
Detonator-*
Screwed Plug
FIG.3
The German " disc " percussion grenade (fig. 3) is designed so
as to act in any position of fall. IL has internally six radial chan-
nels, 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 uritil 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
