they can support it in local combats. If the resistance becomes obstinate and beyond the power of infantry and field guns to overcome, the bombardment by the heavy artillery must be renewed.
These tactics are repeated as each successive line, or defen- sive zone, is encountered. The process can be repeated indefinite- ly so long as the supply of men, guns, and ammunition can be kept up, provided that it is possible to convey them to the fighting line. The latter has proved a very serious difficulty in the past, and has perhaps been more instrumental than any other cause in bringing great attacks to a standstill. It must be overcome by the work of the engineers in repairing roads and railways, and by the provision of improved cross-country vehicles.
Artillery in Defence. Whether defence in the hitherto ac- cepted sense is or is not the form of resistance best suited to modern conditions is a question which lies outside the scope of this article. For the present purpose it is assumed that the ground occupied is to be defended in the literal and tactical sense.
In the ordinary defence of a position the method of meeting an attack varies according to the degree of certainty with which the enemy's intentions have been anticipated, and the amount of preparation which it has been possible to make.
If the defender is fully prepared for the attack, and has massed his artillery to meet it, then he can reply to the initial " intense " bombardment with a similar bombardment, which will certainly render the attack ineffective.
If he knows when the attack is to be launched, but has not been able to reenforce his artillery, he can still put down a preventive barrage, just before " zero " hour, on the enemy's lines. This will weaken the attack, and may delay it.
Even if the defender has had no warning, and is unable to oppose gun for gun to the attack, the mobility of motor artillery should, in future, enable him to reenforce his artillery (provided he has guns available elsewhere) within two days at most. But the enemy will probably provide against this by making a holding attack on a very wide front, or on several fronts. The defender will be uncertain as to which of these is the real attack, and will be afraid to take any guns out of the line. He must then depend upon his general reserve for the artillery reenforce- ments which he requires.
We will consider the case of a section of an entrenched front, held with the normal proportion of artillery (one gun to 30 yd.), attacked by surprise by a concentrated force (one gun to 10 yd.). It is clear that the attacking infantry must come out into the open when they advance, and that they are then exposed to artillery fire. Putting down a shrapnel barrage at 10 seconds' notice on the enemy's front line, and bringing it back over one's own lines when necessary, is of course part of the regular routine of trench warfare. But the attacker counts on destroying or neutralizing the guns of the defence by his bom- bardment and counter-battery fire, and he is likely to succeed to a great extent as regards batteries which have previously disclosed their positions by firing. It is therefore necessary to have " silent " batteries in the line, that is to say, batteries which, ordinarily, are never allowed to fire except on occasions when visibility is bad, and then only under precautions against sound-ranging. The normal expenditure on a divisional front may be i ,000 rounds a day, or less on quiet fronts, and this allow- ance can be fired by a small number of batteries, so that there is no difficulty, other than the administrative one, in keeping half the guns of a front in silent positions in reserve to repel an attack.
Another necessary precaution is the provision of deeply buried telephone cables, proof against bombardment by heavy artillery; and these must be laid not only to the ordinary gun and observing positions, but also to the positions in rear to which the artillery may have to retire.
As soon as the attacker begins his " intense " bombardment the guns of the defence reply with a similar bombardment, necessarily on a scale corresponding to their smaller number.
" Silent " batteries take part in this, since the smoke of the bom- bardment will conceal their positions. When the infantry at- tack is launched, then, assuming that the defender has still a fair number of batteries effective, as soon as the call is made upon them the field guns and trench mortars of the defence put down a heavy barrage on the enemy's front-line and com- munication trenches. Medium guns and field howitzers barrage probable assembly points, while medium and heavy howitzers bombard the attacker's gun positions, so far as these have previously been disclosed. Since the defence has been weakened by the bombardment it is probable that the attacker will capture the forward zone. It takes one gun per 20 yd. to make a heavy barrage; the defender starts with only one gun per 30 yd., and may be reduced to one gun per 60 yd. at the end of the " intense " bombardment. Of these at least a third will be firing on the attacker's guns and communications, so that the defender's barrage will presumably be too thin to stop a determined attack, though it will cause a considerable number of casualties.
For this reason the defender will probably elect to use a partial barrage, that is to say, a barrage of effective density, covering only part of his front, the remainder being protected by machine- guns and trench mortars. If his telephone communications are thoroughly reliable he may be able to control this barrage so as to put it down, at a moment's notice, in front of any part of his line that is attacked. Each battery will then have, say, three alternative sets of barrage orders, so that the whole barrage can be put down on any one of three sections of the front. But this method is so complicated and so liable to break down that few commanders would care to trust to it.
As the attack gains ground the defender endeavours to keep his counter-barrage on the leading troops of the attack, and behind his retiring infantry; but owing to the inevitable break- down of communications while the infantry are on the move it is not likely that this ideal will be completely achieved. When the defenders retire from the second zone of defence the attack will be getting within rifle range of the defender's field guns. The defender cannot afford to lose the whole of his field guns, but it is desirable that some of them, say one-third, should remain in action till the enemy is within 500 yd. of them, as they will cause heavy loss by their point-blank fire. If well supported by the guns which have already retired they have an excellent chance of getting away. As the retirement continues the medium and heavy pieces have to withdraw to the positions prepared for them in rear.
There are many details, such as the support of local counter- attacks and the protection of " strong points " which have held out against the attack, which cannot be entered upon here. Speaking generally, the object of the defender when attacked by a greatly superior force is to maintain an orderly retirement, with his line bending back but never breaking, taking heavy toll of the attacking infantry at every stage of their advance, until the attack is sufficiently weakened, or the defence sufficient- ly reenforced, to enable the defender to launch a general counter- attack.
Enfilade Fire. It has often been suggested that the best artillery defence is that afforded by the oblique and enfilade fire of guns from adjoining sectors of the front. This theory broke down in practice. During sedentary warfare every division had enfilade sections es- tablished in its neighbours' territory, or else had a " call " on some of its neighbours' guns for enfilade purposes. So long as the line was not seriously bombarded these guns were very useful. But when the line was attacked in force it was quite hard enough to keep up com- munication from front to rear within a divisional area, and it proved impossible to direct the fire of the guns of other divisions. These often joined in on their own account to help a neighbour when they could see what was going on, but their assistance could not be relied on as part of the scheme of defence.
Within the divisional front the method of enfilade fire at short ranges is constantly employed; every one of the detached trenches and other works which constitute a defensive zone should be enfiladed from works in rear of it, and the approaches to it should be swept by oblique fire. This duty is chiefly performed by machine-guns, but it is advisable, when possible, to provide the batteries in rear with extra emplacements from which guns can fire obliquely or even across their front.
