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Rh Registration. The reenforcing guns must be able to open fire at zero hour. Usually the batteries belonging to the front register their targets for them beforehand, the registration being spread over several days so as not to attract special notice. But calibration, study of atmospheric influences, and surveying 1 have latterly been so thoroughly applied that it may be possible, in future, to rely upon opening effective fire by map without ranging. This again requires thorough preparation, which is possible when an attack is planned beforehand. So far as can be foreseen-* there is no prospect of dispensing with ranging when the troops are on the move.

Conduct of the Attack. Bombardment. In the great trench battles of 1916 and 1917 it was customary to begin with a bombardment of the enemy lines lasting ,a week or even more. This was fatal to surprise action, and in 1918 the preparation consisted of some six hours or less of " intense " bombardment, every gun firing at its highest rate. The use of tanks may in future enable this bombardment to be shortened, as will be seen. The Germans pressed their great attack, of March 1918, only on alternate sectors (of about 3,000 yd.) of the British line, trusting to envelop the intermediate sectors. They were thus enabled to concentrate nearly the whole of their guns on half the total frontage, so that they had roughly one gun firing on every 5 yd. of the front actually attacked.

A reasonable estimate of the ammunition required for a six hours' intense bombardment per mile of front seriously attacked is 50,000 rounds field gun ammunition, 10,000 field howitzer, 5,000 6-in. howitzer, 2,000 6-in. gun, 500 heavy howitzer, and 200 rounds superheavy howitzer. If the attack presses forward without a check for three days from the start, then at least 50% more will be required on the second day, and the same on the third day if the enemy is reenforced; at any rate it would be unwise to begin an attack without double the above amount in hand. If the attack is seriously checked the intensive bombardment will have to be repeated and a fresh start made. These figures give a fair idea of the scale on which guns and ammunition are used in modern warfare.

The reason for this vast expenditure of ammunition is that the bombardment is not confined to the front of the position at- tacked the front zone, as explained above, is a thinly held system of outposts it is directed mainly on the real defensive zones and centres in rear. Targets such as railway stations, bridges, and road junctions as much as 10 m. behind the front have to be bombarded by the long-range guns and howitzers.

Influence of Tank Action on Bombardment. In the autumn of 1918 the tanks achieved such success in breaking through defences which had not previously been bombarded that it is considered that in some cases, provided that the ground is favourable for tank action, it may be possible to shorten the preliminary six-hours' bombardment to half-an-hour, or even to dispense with it altogether, and to trust to the creeping barrage to protect the advancing infantry and tanks (British Field Service Regulations, 1920, Part II., para. 118 [6]). When this method is employed all guns other than those firing the creeping barrage will concentrate on important points behind the enemy's front simultaneously with the launching of the attack.

This is a new method of procedure, in which our present experience is not sufficient to enable us to forecast the best course of action with any confidence. The regulation quoted above is cautiously worded, and does not imply that the use of tanks will render bombardment unnecessary. Even if the tanks are expected to succeed in rushing the first and second zones of the enemy's defences, they will certainly experience increased resistance as they penetrate deeper into the position. In future warfare tanks will not be the only motor vehicles on the battle- field. The mobility of the defender's motor guns and motor in- fantry, both on and off the road, will enable him to bring up reenforcements far more quickly than was the case in 1918. Al- though the attack may be launched without any previous bom-

1 The position of one gun in each battery (or other unit) is fixed exactly by survey and marked both on the map and on the ground before the guns arrive.

bardment, it will still be necessary to deliver a heavy fire on targets behind the enemy's front as soon as the attack is disclosed. It will not be enough to' bombard railway stations and road junctions if the defender's motor troops are independent of railways and roads. Therefore this fire will presumably be not so much a bom- bardment of fixed points as fire for effect, directed by aeroplane observation, upon the defender's reenforcements.

So far as can be judged the amount of ammunition required for an attack will be increased rather than diminished, in view of the scattered targets presented by motor troops.

The Infantry Attack. As soon as the " intense " bombard- ment has done its work on .the outpost zone and the first line 2 the infantry advances, screened by a creeping barrage, pre- ceded by tanks, and closely followed by guns of accompaniment. The bombardment is " lifted " from the first line to reenforce that on the second line; as soon as the infantry have taken the first line fresh waves of men pour through them to attack the second line. When the second line is taken the field artillery of the attack pushes forward by echelons to positions in or near the first line. Later on the medium and heavy artillery push forward.

It is not to be expected that the infantry will be able to ad- vance on a continuous front. After the thinly held outpost system has been rushed progress is by " infiltration." Wherever a weak point is found the infantry pour through it, and the ad- vancing streams of men, fed by the local reserves, spread out to right and left and envelop the defensive points that still hold out. Tanks are here invaluable in leading the streams of riflemen, in " rolling out " barriers of barbed wire, and in rushing the centres of defence. It is the involved and complicated nature of this warfare which prevents the main body of the artillery in rear from supporting the infantry in the series of local combats which characterize the. advance through the trench system, and which renders it necessary to provide the infantry with guns of accompaniment.

The process of infiltration outlined above is apt to produce irregular salients in the advancing line, which the artillery in rear find it difficult to protect by barrage, and which are there- fore the more exposed to counter-attack. On this account it was the practice, at one time, to limit the objective that is, to fix a line beyond which the troops were not to advance, so that when this line was gained they should present a continuous front, protected by artillery fire, from which a further advance could be made. This system led to a great waste 'of opportunity. It may still have to be adopted on occasion; but the modern tend- ency is to gain every possible foot of ground, and to provide reserves on a scale sufficient to " feed " the salients so that they can spread out laterally and " pinch out " the ground between them which is still held by the enemy. That is, every salient must become an offensive, not a defensive, feature. Without artillery support these offensive tactics would hardly succeed against the defender's " strong points," which are not merely fire-trenches facing the front, but miniature forts prepared for all-round fire. It is necessary, therefore, that in addition to the guns of accompaniment part of the artillery in rear should press forward boldly, so as to keep in touch with the infantry and be able with the assistance of aeroplanes or of their own recon- noitring patrols to direct a heavy fire on any defensive work which still holds out.

The action of the artillery in the attack may be summed up as follows: the bombardment weakens the defence and the barrage protects the attack. The guns of accompaniment sup- port the attack so long as the enemy continues to retire, offering only slight resistance intended to weaken the attack. When resistance becomes serious the divisional field artillery must be in position and in communication with the infantry, so that

2 The word " line " is used in this description because no other accepted military term is available. In reality modern defensive systems consist of chains of detached works or trenches, supporting each other by their fire. The only continuous feature which marks a defensive zone is the belt of barbed wire entanglement, and this itself is irregularly traced.