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262 war requirements. The weight of the shrapnel bullets contained in a shell can therefore be increased only at the expense of their number. In the other direction, the minimum weight of the bullet is de- termined by the necessity for providing sufficient disabling energy. It has been found experimentally that a striking energy of 60 foot- pounds is sufficient to disable a man. In the case of a bullet starting from the point of burst with an initial velocity of 1,000 fs., as in the British i8-pr. at 4,ooo-yd. range, the striking energy after it has travelled 300 yd. is as follows:

Weight of Bullet.

Remaining Velocity.

Striking Energy.

France Russia Germany

38 to the pound 43 " 45

388 fs. 378 " 370

61-5 foot-pounds 52-8 " 47-2 " "

It will be seen that under the assumed conditions the French bullet of 38 to the pound is the only one which provides sufficient striking energy at 300 yd. from the burst. Of the nations which took part in the World War, the French, the Japanese, and the United States (who had the French equipment) were the only ones who used the heavy shrapnel bullet. The other nations (except the Russians) considered that the trajectory of their guns was not flat enough to carry a good proportion of the bullets to a distance of 300 yd., and consequently preferred lighter but more numerous bullets which gave a closer pattern over a shorter distance. It would seem that the Russians, with their powerful gun, would have done better to use a heavier bullet.

Technical Employment of Shrapnel. A shrapnel should be burst in air so that the axis of the bullet-cone passes through the centre of the target. This is a matter of ranging, and is dealt with elsewhere. Further, the distance of the point of burst from the target should be such as to produce the greatest possible effect. This also is a matter of ranging, but the gunner must first know what is the correct distance which he has to attain. This is determined by theory.

The target surface of a man, measured at right angles to the trajectory of a shrapnel bullet, may be taken as % sq. yd. when standing, J sq. yd. when kneeling, and \ sq. yd. when lying or firing over a parapet. The best effect is produced when the density of the cone of bullets is such as to provide one effective bullet for each man. The density depends on the target surface offered by each man; it is immaterial, as regards the best distance of burst, whether the men are in a thin skirmishing line or shoulder to shoulder. If the distribution of bullets throughout the cone were uniform that is, if the shrapnel gave a perfect " pattern " then at standing infantry the cross section of the cone should contain one bullet per J sq. yard. Taking a shrapnel containing 300 bullets, the cross sec- tion of the cone at the target would have to be 150 sq. yards. The apex angle of the cone being aboufl in 4, this would fix the best dis- tance of burst at 55 yd. from the target. But the distribution of bullets in the cone is not uniform. If it be assumed to be haphazard (which is nearer the truth), then, according to the Theory of Prob- abilities, the probable maximum effect is produced when the cross section contains 1-24 bullets for each man. This gives the best dis- tance of burst for the above shrapnel as about 50 yd. against standing men, 41 yd. against kneeling men, and 35 yd. against men lying or firing over a parapet. With the shrapnel of the British l8-pr., which contains 375 bullets, the best distances are 55, 45 and 38 yd. respectively.

The question of the distance of burst is affected by the error of the fuze. If, for instance, the fuze be such that the shrapnel is liable to burst 60 yd. over or short of the desired point, then if this be fixed at 40 yd. from the target some of the shrapnel will be wasted by bursting on the ground. Similarly, the error of the gun will cause " short " rounds to burst on the ground. In the British and in the French services it has been laid down that the distance of burst for field guns is to be such as to appear from the battery 10 minutes of angle (in French notation 3 " mils," i.e. yifeo of the range) above the target. This corresponds to a distance of burst of 70 yd., and rather less at longer ranges, and gives about 10% of bursts on graze. This distance has been fixed partly with reference to the error of the fuze (which, under war conditions of manufacture, is considerably greater than in peace time), but principally for simplicity. When good fuzes are available better shooting is to be obtained by adhering to the theoretically correct distances given above. Towards the end of the war the Germans used a number of very accurate mechanical time fuzes, and if these come into general use the service height of 10 minutes above the target will no doubt be reduced.

Penetration. Even the heavy French shrapnel bullet will not pierce the thinnest of the steel gun-shields in use, and it is quite ineffective against infantry shields, loophole plates, and the plates of a tank. These shields are all made to resist infantry bullets, which have much greater power of penetration than leaden shrapnel bullets. Steel shrapnel bullets will pierce gun-shields if the shrapnel be burst ^close up. 1 As the steel bullets are larger than leaden bullets of the same weight, their use entails a reduction of about 20% in the number of bullets in the shrapnel. For the same reason they do not fly so far, and shrapnel filled with them are less effective against

1 These were actually used to a small extent by the Germans towards the end of the war, possibly on account of shortage of lead.

infantry. Tungsten steel bullets containing 14% of tungsten would be as heavy for their size as bullets made of the ordinary lead-anti- mony alloy, but difficulties of expense and supply will probably prevent their introduction.

Percussion Shrapnel. Shrapnel are invariably fuzed with time- and-percussion fuzes, constructed to burst either in air or on graze. The object of the percussion arrangement is almost entirely to assist ranging by giving visible bursts on the ground. The bullet-effect of shrapnel burst on graze is negligible, as the shell rises steeply from the crater before it opens, and the bullets are blown out in an upward direction, and lose their effective velocity before coming down again. Occasionally the ground may be so hard and the angle of impact so small that the shell ricochets low instead of forming a crater and shower, viz. upwards. But generally speaking percussion fire with shrapnel at troops in the open is a waste of ammunition.

When a direct hit on a gun-shield is made with shrapnel shell the shell does not open till it has travelled several feet further, unless it hits the gun or some solid part of the carriage, and there is no bullet- effect on the detachment. As a rule, a direct hit from a field shrapnel on a modern cellular ammunition box does not blow up the contents, though it may explode a H.E. shell if it makes a fair hit on it, and it may set fire to some of the cartridges.

When percussion shrapnel are fired at a building the shell explodes as it passes through the wall, and produces good bullet-effect on anything behind, as in this case the check is sufficient to give the base burster time to ignite. It used to be held that troops were safe from shrapnel behind two walls, and this is literally correct ; but there are so many windows in the front of a house that the shrapnel is liable to pass through them and burst through the back wall, and moreover, under the fire of powerful modern field guns the front wall soon ceases to exist.

Owing to the charge of black powder which it contains shrapnel has considerable incendiary effect on buildings.

Howitzer Shrapnel produces its characteristic effect by the bullets striking downwards at a steep angle 40 degrees or more to the horizontal. The object is to reach troops behind a parapet or gun- shield. The depth of effect, being proportionate to the cosine of the angle of impact, is much less than with a flat-trajectory gun. Precise ranging and an accurate fuze are required to produce good effect. During the first or mobile phase of the war shrapnel fire from field howitzers gave excellent results; later, however, the difficulty of procuring good time fuzes for howitzers brought this class of shell into disrepute, and it seems probable that its use will be discontinued except for light field howitzers, and even in these reserved to mobile warfare.

The theory of the effect of howitzer shrapnel is the same as for gun shrapnel. The weight of the bullet is increased to compensate for the low remaining velocity. The angle of descent of the lowest bullet, including half the angle of opening, is about 40 degrees to the horizontal, so that a man would have to crouch very close behind a gun-shield or parapet to escape being hit. When burst at effective height a field howitzer shrapnel, such as that of the British 4'5-in. howitzer, covers a space 35 yd. wide and 70 yd. from front to rear.

Universal Shell. These are combined shrapnel and howitzer shell; a type is described and illustrated in 1.869. The idea is that when burst in air at shielded guns the head flies forward and acts on impact as a small H.E. shell, powerful enough to disable the gun if it strikes it, or to reach the men behind the gun-shield with splinters flying sideways or even backwards, while the body of the shell acts as an ordinary time shrapnel. If the whole shell is burst on impact it detonates like a H.E. shell. Such shell were used in the war, but their usefulness was always a matter of controversy and their com- plicated design made supply difficult.

High-Explosive Shell. These were the principal projectile fired by all natures of land artillery during the long period of trench warfare in the western theatre of war. They are of two kinds, thick- walled shell and mine shell. The former have a comparatively small burster and are intended to kill men with their splinters; the latter are thin-walled shell containing a large burster, and are intended to penetrate deeply before bursting, and to destroy fortifications and material. Mine shell are fired from howitzers, in which they are exposed only to a low pressure in the bore. In modern howitzers, which are required to range at least 50 % further than those in use in 1914, the endeavour is made to keep down the pressure as far as possible by increasing the length of bore, thus getting more work out of the same charge. But the increase of range which can be obtained in this way is hardly sufficient, and heavier charges are inevitable. Mine shells for such pieces have to be made thicker in the walls to prevent them from collapsing in the bore, and tend to approximate to the thick-walled type.

Thick-walled shell are almost always fired with instantaneous per- cussion fuzes; occasionally they are fired with time fuzes to burst in air. The object of the instantaneous fuze is to burst the shell on the surface of the ground before it has time to penetrate, so that the splinters are not wasted by being smothered in the crater. Thus, early in the war, the German howitzer shell, for want of an efficient instantaneous fuze, used to penetrate deeply into the soft clay of Flanders, and the result was a vertical eruption of mud and splinters which was harmless to men not actually on the spot struck. Instan- taneous fuzes are also used to burst H.E. shell in the act of passing