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252 battle zone, and to delay an attack long enough to allow the battle zone to be manned.

The field artillery have three sets of positions, known as for- ward, main, and reserve. The forward positions are in the battle zone, and the guns posted there are intended to protect the out- post zone, and to support minor attacks made from this zone (see p. 253, Warfare between Front Trenches). The main positions are 3,000 to 4,000 yd. behind the front trench, that is, in the re- serve zone, some 1,000 yd. behind the second-line trench; the guns posted in the main positions barrage the front trench and support the infantry in the battle zone. The reserve positions are 3,000 to 4,000 yd. behind the second-line trench, and the guns, when they occupy them, barrage the second-line trench and support the infantry in the reserve zone.

Normally about one-third of the divisional field artillery are in the forward positions and two-thirds in the main positions. The reserve positions are ready for occupation and supplied with ammunition. 1

The medium and heavy artillery are behind the field artillery, and the wagon lines are out of field-gun range, that is, at least 5 m. from the enemy's field artillery positions. Additional artil- lery positions are prepared, so far as the supply of labour per- mits, for reenforcing units, which are put in when it is intended to attack, or when an enemy attack is threatened. All guns normally belonging to the front are in emplacements provided with overhead cover, and carefully camouflaged against the camera. All fire trenches and entrenched posts (called " strong points ") are protected by entanglements of barbed wire. Artil- lery observing posts (" O.P.'s ") from which the fire of the bat- teries is directed, are disposed wherever they can be concealed, and the whole system is connected up by an elaborate network of telephone wires, the main lines being (in British practice) deeply buried.

The arc of fire required of each battery has to be considered when siting and entrenching it. The following is a typical arrangement, subject to considerable local variation. It applies to a division of three infantry brigades of four battalions, three field-gun brigades of four batteries, and one field-howitzer brigade of four batteries. Each infantry brigade holds one unit of front, about 1,000 yd., and is supported by one field-gun brigade. Of the four batteries of this brigade, three cover their own unit of front and can cover one more unit on each side, making 3,000 yd. of front; the fourth battery is a " swinger," and covers two units on each side of its own unit, making 5,000 yd. of front. All the field-howitzer batteries are swingers. This arrangement enables the division to turn 13 field batteries on to any point on its own front, and to turn 6 field batteries on to the front of either of the neighbouring divisions when called upon. The medium, heavy, and super-heavy guns and howitzers are all sited, when possible, so as to engage any target within their range. .

Under these conditions, as soon as trench warfare began, artillery fire became a matter of very careful preparation and rapid execution. A battery was liable to be called on suddenly to fire on any one of a hundred different targets, visible from an O.P. or not. The first essential was to get every gun to shoot to map range. In open warfare, artillery firing at visible targets neglect the " error of the day " due to variations of temperature, barometric pressure, and wind, since this is corrected by direct observation of fire. In the trenches this error became of great importance; it might, and did, make the difference between hitting the enemy or our own infantry. The daily " Meteor " telegram from the meteorological section of the army corps was supplemented by reference to the thermometer and wind-gauge whenever a battery opened fire. Worn guns were carefully " calibrated " so that their error could be allowed for; this was

1 The British, who used 6-gun batteries, used to keep two guns of a battery forward and four in the main position ; with 4-gun batteries it is not usually advisable to split them up. The Germans used to keep the whole of their field guns in the main and reserve positions, and these were further back than those described above; guns were sent up to the advanced positions for special tasks only, and were with- drawn as soon as these had been completed.

done at special ranges behind the front, or, when this could not be done, by firing at known points in the enemy's lines. The next matter was to obtain an accurate map, with the positions of the batteries and their targets marked on it, so as to enable the exact map range to be measured. 2 The result of this work was a great improvement in shooting, and consequent economy of ammunition. Unfortunately the varieties of powder supplied caused a further complication. It proved impossible to distribute the ammunition so that each brigade had always one particular nature or brand of powder, except on special occasions, when preparations were made for a great attack. It was therefore customary, in trench warfare, to " register " all prospective targets, or at least points near them. 3

Howitzers. The necessity for searching deep trenches and penetrating overhead cover gave rise to a demand for more howitzers. The field gun, firing shrapnel, was invaluable when the enemy moved about their trenches, or showed themselves over their parapets; at other times shrapnel was of little use, except for barrage. The field gun H.E. shell was too small to penetrate parapets, and the field-howitzer shell did not penetrate well-built dugouts. All the belligerents found that the most useful weapon for bombardment was the 6-in. (15 or 15-5 cm.) howitzer, throwing a shell of 100 pounds. The Germans in par- ticular regarded this as their most important weapon for trench warfare. In 1914 the British army had only a few old-pattern 6-in. siege howitzers, but from 1915 they had a 6-in. Q.F. howitzer ranging 10,000 yd., which range was afterwards in- creased to 1 1, 600 yd. by the issue of stream-line shell. By the end of the war the British had 6,437 howitzers in France alone; 3,633 6-in. howitzers had been issued, and 1,458 were in the line on Armistice day, which shows the rate at which they were worn out. They fired over 22,000,000 rounds.

Similarly in 1914 the French had only 300 howitzers of 155 mm., of which 104 were mobile. In 1918 they had 6,000 of this, and larger calibres.

The heavy and super-heavy howitzers, 8-in. (21 cm.), 9- 2 or 9'4-in. (24 cm.) and higher calibres were used for work too- heavy for the 6-in.

For all calibres over 6-in., howitzers soon began to supersede guns, though a few flat-trajectory heavy guns were used. The reason for this was a question of supply. A howitzer firing at 45 gets its shell to the target with a much smaller powder charge than a high-velocity gun, and consequently lasts perhaps 10 times as long before it has to be retubed.

Increased Range. The precision with which " map fire " could be carried out by the methods described above led to head- quarters, wagon lines, ammunition " dumps^" and installations behind the lines being shifted to greater distances from the front. This created a demand for increased range. When the Germans initiated the system of covering the front with a zone of " pill- boxes " and small posts, and withdrawing the front trench (or its equivalent chain of short trenches) a mile behind the front of the defended zone, the ranges were still further increased. Even before this, the Germans had lengthened their field gun and brought out a stream-line shell which increased its range from 6,000 yd. to 11,700 yd.; their old field howitzer ranged 7,600 yd., their 1916 pattern 10,500 yd., and similarly with the 6-in. howitzer and larger calibres. Other nations did the same; the French altered the trail of their 75-mm. field gun so as to get more elevation and increase the range to 11,000 yd. with stream-line shell, and introduced their short ig-cm. gun, converted

2 This resurvey often showed local landmarks to be 100 or 200 yd. from their positions as marked on the original maps.

3 Registration consisted of firing a series and noting the result, corrected to standard " Meteor conditions. These series were observed from O.P.'s when possible, otherwise by aeroplanes or sound-ranging. Thus when an enemy working party was reported by an aeroplane in Trench 56, a battery commander got the order " Target 56 stop 25 shrapnel 25 HE Fire." He looked up 56 in his registration book, corrected the recorded elevation, direction, and fuze for " Meteor " and powder in use, gave his orders, and his guns fired the 50 rounds in half a minute. The aeroplane observed the result, which was entered in the registration book for future reference.