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264 Penetration of Tank Armour by 28-pr.

Range yards.

Thickness of Armour Penetrated inches.

Weight of 10 square yards 1 of Armour tons.

1,000

2,000 3,000 4,000 5,000 6,000

2-331 914

633 520 409 323

3-902 3-204 2-798

2-544 2-360 2-215

The effect of armour-piercing shell, fired from high-velocity guns, in penetrating armoured turrets and cupolas, is given by the same formula. As an example, a 30-5-0111. (i2-in.) gun may be expected to pierce the following thickness of hard-faced armour : Range, yards. . 5,ooo 10,000 15,000 20,000 25,000

Penetration, inches 12-5 9-25 7-5 7-25 7

At 6,000 metres the 24o-mm. gun penetrates 180 mm., and the I55-mm. G.P.F. gun penetrates 77 mm.

The cupola must be massive as well as stout, or else the effect of the blow will be to displace it and jam the rotating machinery, even if the shell does not penetrate. In the Liege and Antwerp cupolas, which were intended to resist 6-in. guns, lead cushions were used to reduce the " racking " effect. A small cupola of three metres in diameter cannot be expected to stand blows from heavy shell, though it may be stout enough to resist penetration. The striking energy of a 12-in. shell at 5,000 yd. is about 20,000 foot-tons.

At the beginning of the war, a fort was at a disadvantage in that its position was known, whereas it was fired on by long-range guns which could not be located, unless the aircraft of the defence retained the mastery of the air. The development of sound-ranging helps the defence in this respect, provided that the instruments can be set up in several forts connected by telephone.

VII. EFFECTS OF COLLECTIVE ARTILLERY FIRE

These vary, so much according to local and tactical con- siderations that no exact rules can be laid down. However, the following were rough working rules established during the war:

Standing Barrage. To keep down the fire of riflemen in a trench, each man should be liable to be killed if he shows himself above the parapet at least once a minute; therefore one shrapnel per minute should be burst in front of him. Taking the effective spread of shrapnel bullets at 25 yd., then 4 rounds per 100 yd. of trench are required. This is an ordinary " barrage, and may be changed to a " heavy " barrage of 8 rounds a minute or a " light " barrage of 2 rounds a minute per 100 yd. as required. If a 4-gun battery has to barrage a trench of 300- yd. front, then at the " ordinary " rate each gun will fire 3 rounds a minute, distributed over the 75 yd. allotted to it. To barrage a communication trench " end on, ' 2 rounds a minute per 100 yd. of length are sufficient, when the line has been corrected to bring every burst over the trench. It is not necessary to barrage the whole length of a communication trench, which may be 2 m. long; aeroplane photographs show the most effective barrage points, namely the " defiles " at which there is no way round. Communication trenches may be so effectively barraged as to oblige the enemy to risk the chance pf coming and going across the open.

Creeping Barrage. This may be of several different kinds, as described above. With time shrapnel, or a mixture of H. E. and smoke shell, fired from field guns, a battery can efficiently barrage a front equal to its own normal front, or 20 yd. per gun. (The French reckon 15 metres per gun.)

In the British service the normal barrage rate was 4 rounds per field gun per minute for 2 minutes, then " lift " to the next range and repeat, and so on. On emergency a battery can cover a wider front for short periods; the comparatively slow rate of fire is due to the constant changes in elevation and setting of fuze, and possibly in direction as well. However, this rate amounts to 240 rounds an hour per gun, which is about as much as a battery can do.

The French reckoned 2 rounds per 15 metres of front per minute for a " heavy " barrage, down to the same per 45 metres of front for a " light " barrage. The Germans, in 1918, advanced their barrage by " bounds " of 200 metres for field guns and 400 for medium guns and howitzers; after each bound the guns continued to fire at the same range (" pounding ") for some minutes. Owing possibly to worn guns, the German barrage was considered less dense and less effec- tive than that of the Allies, although the nominal rate of fire was higher.

When firing a barrage with time shrapnel, the bursts must be kept low, and a setting of fuze giving 50% of bursts on graze is considered the best. With H.E. shell instantaneous fuzes are best, unless there are no smoke shell in the barrage; in this case it may be better to use normal fuzes, in order to throw up more dirt and make a more opaque screen.

Bombardment. It is found that a 'field H.E. shell displaces 4 cub. metres of earth per kg. of burster, or 2| cub. yd. per pound.

1 A tank armoured in front only may require some 10 sq. yd. of armour.

With larger calibres the effect increases in a somewhat higher ratio. But the number of rounds required for a given task cannot be ascer- tained directly from these premises, since much of the effect of sub- sequent shell falling in or near the same place as the first shell is wasted by displacing the earth already lifted, which has fallen back into the crater. A more reliable guide is the diameter of the crater, which varies according to the soil. In ordinary ground a 6-in. howitzer mine shell, containing some 13 Ibs. of H.E. makes a cylin- drical crater about 4 yd. wide and 3 yd. deep, of which depth about one-third is filled up by earth falling back into it. Hence to destroy a 12-ft. parapet it must be struck by one 6-in. shell per 4 yd. of front. If a calibre be employed which gives a crater of less diameter than the thickness of the parapet, this will entail a great waste of ammu- nition. Thus the French found that under practice conditions of accuracy it took II rounds of field-gun shell per yard to breach a parapet 10 ft. thick, or perhaps 20 rounds a yard under war condi- tions. Therefore they consider that for practical purposes a lo-ft. parapet is proof against field guns and 4-2-in. field howitzers.

At stout brick and concrete walls, H.E. shell with " normal " fuzes (i. e. neither instantaneous nor delay action) are very effective. A wall 20 in. thick is cut down by an expenditure pf two or three field gun shell per yard. A field-gun shrapnel will pierce a wall of this thickness at medium range.

At field guns in the open, the French reckon 15 rounds of field-gun shell at 3,000 metres, or 25 rounds at 3,500 metres, to make a hit on a gun. The British l8-pr., under experimental conditions, is capable of making 60% of hits on a gun in action at 2,000 yd., 16% at 3,000

Fd., and 5% at 4,000 yards. Medium guns such as the 6o-pr. or rench 4-2-in. maintain their accuracy to longer ranges than field guns; a rough rule is to add one-third to the field-gun range for the same percentage of hits; thus a 6o-pr. is capable of making 16% of hits on a gun at 4,000 yards.

The following experimental results (Krupp) show the comparative effects of various natures of field-gun and field-howitzer shell fired at a battery of four guns in action, a wagon beside each gun :

(a) H.E. field-gun shell, percussion fuze. Range 5,000 metres. One hundred rounds disabled I gun, i wagon, and n dummy men out of 34.

(6) The same, time fuze. One wagon damaged, 4 dummies put out of action.

(c) The same target, range 2,000 metres, fired at with 4'2-in. howitzer (presumably similar to the German service field howitzer). Time shrapnel. Twenty-four rounds fired after ranging had been completed with 1 1 rounds percussion. Result, 26 dummies put out of action out of 34.

A heavy discount must be taken off these experimental results for war conditions, especially in view of the quality of war-time fuzes. However, the general inference is that percussion H.E. shell is a much better projectile to fire at a battery in the open than time H.E. shell, and that field-howitzer time shrapnel is remarkably effective when the range and fuze can be correctly found, though it probably takes much longer to produce effect with it than with H.E. shell. In duels between field batteries, such as often unexpectedly occurred during the war, it is all-important to knock out the enemy's guns as quickly as possible, and percussion H.E. shell with instantaneous fuze is the best projectile to use.

Wire Cutting. The development, during the war, of the methods of cutting barbed wire by the fire of artillery has already been described. With the British l8-pr. at ranges of 600 to 1, 800 yd., a belt of ordinary barbed wire entanglement 8 yd. deep can be cut through with an expenditure of about 10 yd. of time shrapnel per yard of front. The process is slow, as very precise shooting is required. A better projectile is 4-5-in. howitzer H.E. shell with instantaneous fuze; each effective round, at ranges up to 6,000 yd., clears a circle about 3 yd. in diameter. Howitzer H.E. shell with normal or delay-action fuze makes a crater into which the network of wire falls back, and so makes a worse obstacle than before. A 52-lb. trench mortar bomb with instantaneous fuze clears a circle 5 yd. in diameter. The French in 1918 used field guns firing H.E. shell, either with instantaneous fuzes or with a slight delay action to burst the shell on ricochet. The lines of fire were 5 metres apart at the target. At a belt of strong wire 25 metres deep it was found that 600 rounds were required to clear a lane 25 metres wide. The ranges were from 2,000 to 4,000 metres. Tanks, when available, are much better wire-destroyers than artillery.

Fire with Star Shell. These are used for illumination, and are usually fired from field howitzers. They must be burst at such a height that the stars burn out before reaching the ground ; otherwise they form a smoke screen on the ground, besides setting fire to dry vegetation. A star shell, properly burst, lights up a circle about 50 yd. in diameter effectively, and patrols are distinguishable up to about 100 yards. For continuous illumination, four shell per minute per 100 yd. of front gives good results. (See also, generally, the article ORDNANCE.) (H. A. B.)

ARTOIS, BATTLES IN (1914-7), see Plates I., II., III. and IV. (A) (. 30-. 8 1914).—After the stabilization of the battle-front on the Aisne and to the E. of it, about Sept. 16, both the Allied and the German Higher Commands