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troops that are firing on them, it is the more necessary that they should at least screen them from aimed fire. Therefore, the artillery barrage has become a feature of mobile as well as of trench warfare. Tanks also require to be screened by a barrage, although this, since it is not required to destroy opposition, may consist of smoke shell, of which a relatively smaller number suffice to create an opaque veil. Therefore, in a future attack, the artillery must be on hand so that they can be got into action at short notice, ready to form a barrage at once. But the artillery of the normal divisional establishment will barely suffice for the purpose. If it is a smoke barrage that is required, this is pref- erably fired by the divisional field howitzers which are the most suitable weapons. These are provided as a rule on the scale of about 16 pieces per division. If, then, the division attacks on a front of 1,600 yd., this gives only one field howitzer per 100 yd., and at their highest rate of fire (about 10 rounds a minute for short periods, or 100 rounds an hour) they will not be able to form a smoke barrage to cover the whole divisional front, unless the weather conditions be exceptionally favourable. Similarly, for an offensive barrage of shrapnel or H. E., which requires one gun per 20 yd., the 72 field guns and field howitzers of a pre-war division would barely suffice to cover its attacking front, leaving none available for bombardment and counter- battery work. The divisional artillery must therefore be reen- forced for an attack, as in trench warfare, though not necessarily to the same extent.

This reenforcing artillery will be taken, in the first place, from reserve formations. Presumably the highly mobile army re- serve field artillery will be drawn upon first, and then the artillery of the divisions in reserve. It may even be necessary to take field artillery from other divisions in the fighting line. In the days of horse-drawn artillery this would have been a dangerous expedient, but with motor artillery capable of cover- ing 50 m. a day the objections are less serious.

Observation of Fire. When both forces are on the move, there can have been no previous registration of targets. There- fore the medium and heavy artillery, which engage long-distance targets, must use aeroplane observation so far as available. Fir- ing by the map is in mobile warfare a last resource, as there is no opportunity for the survey work characteristic of trench warfare and of the preparatory phase of the break-through battle. The mastery of the air, in order to enable ranging aero- planes to do their work, is of the highest importance.

Change to Trench Warfare. Mobile warfare is liable to turn into trench warfare at any moment; the retreating force, if not vigorously pressed, may have time to entrench a position. And even the advancing force may find it expedient to halt and pro- tect itself by entrenchments when the strategic centre of gravity shifts to another part of the line or even another theatre of war. Therefore an advancing or retreating force must have at hand, so as to be available at short notice, the whole armament neces- sary for trench warfare, from heavy howitzers on railway mount- ings down to trench mortars.

The Defence. A defensive position in mobile warfare differs from a regularly entrenched position principally by the weakness of its passive defences. Belts of barbed wire, deep trenches and dugouts, and armoured machine-gun emplacements cannot be improvised; they require time, labour and material. As regards offensive power, the chief drawback of an improvised position is its weakness in long-range artillery fire, due to the fact that firing by the map requires careful preparation, including survey- ing and mapping from aeroplane photographs. Another weak point is the difficulty of providing reliable communications, since deeply laid telephone cables are not available.

As above mentioned, the position consists of a system or net- work of localities, supporting each other by their fire, and distributed in depth as far as the strength of the force allows; thus a strong force may hold a zone 3 m. deep, with the positions nearest the enemy held just strongly enough to oblige him to deploy. A few horse artillery or mountain guns, supported by machine-guns, afford a sufficient volume of fire for this pur- pose. As the attacker penetrates into this network of small

positions, he finds it increasingly difficult to maintain a con- tinuous line, with or without a barrage in front of it, and he is exposed to counter-attacks, especially from tanks which have been concealed behind cover. If he attacks en regie with an in- tense bombardment and complete barrage, he may find that he has wasted his time and ammunition on a skeleton force. His safest course is to bombard, and assault each strong point in turn. But the defender will avoid the choice of conspicuous localities as strong points; an angle of a hedge affording a field of fire of only 100 yd. is better than a clump of trees on a hill. Many of the strong points will be so inconspicuous that they will have to be located by the advancing infantry and tanks before any considerable volume of fire can be brought to bear on them by the artillery in rear. In principle, the defender's methods are the same as those described earlier in this article, but the absence of the successive definite zones of defence allows of greater flexibility, especially as regards counter-attacks. The attack on an entrenched position is to a great extent a pre- arranged operation based on positive and detailed information. But when the attacker penetrates into the advanced works of a strange position, unfamiliar to him except in so far as the nat- ural features of the country are shown on the map, he ventures into the unknown, and the advantage of surprise attack rests with the defender, if he is bold enough to avail himself of it.

On the other hand, the successful defence of a position in the open unfortified country requires a nice balance of subordinate initiative and higher control, and therefore a degree and quality of efficiency that are not always to be found in a retreating force. (H. A. B.)

V. ORGANIZATION

Before the World War the artillery of the military Powers was organized on the following general lines: Cavalry division, one horse artillery battery per brigade of three regiments, each of 600 sabres. Infantry division of 12 battalions, six field guns (including field howitzers) per battalion of 1,000 rifles. A British division had also one battery of medium guns. Army Corps of two or more divisions, 6-in. guns and howitzers (no fixed scale), and the divisional artilleries. In the French army, a proportion of the field guns which elsewhere were assigned entirely to divisional artilleries was reserved under corps con- trol as " corps artillery." Army of two or more army corps, all mobile guns and howitzers of calibres above 6-in. (few existed) and a siege train when required.

Proportion of Guns to Rifles. The proportion of six field guns per 1,000 rifles was found satisfactory, as a normal scale, throughout the war, but extra field guns from army reserve had to be added for anything larger than an army corps operation. Opinions differ as to the strength at which this reserve should be maintained; it may possibly be fixed at 25% of the divisional artillery.

For trench warfare, the divisional field artillery had to be supplemented by the addition of pieces effective against field entrenchments. These included medium howitzers, notably the 6-in. howitzer throwing a ico-lb. shell, and medium and heavy trench mortars.

Battery Organization. Before 1914, field artillery had in most countries been organized in batteries of four guns. Great Britain (for her regular army), Germany, Austria-Hungary and Italy 1 however, kept to the old six-gun battery. The Russians had a unit of eight guns, which could be used as two four-gun batteries. The four-gun battery is tactically more efficient; it admits of more in- tensive fire-direction, and is easier to lead and to conceal. Moreover, a six-gun battery rarely has occasion to use its full fire-power of 20 rounds per gun per minute, and its guns are not worked to their full capacity; better value, gun for gun, is obtained from the four-gun unit. In Great Britain, on the outbreak of war, all the batteries of the new army were raised as four-gun batteries, as were already those of the Territorial Force. But in 1916 the British army reverted to the six-gun organization; the reason given being the impossibility of providing a full battery cadre of five officers for every four guns. But it is an open question whether that cadre as conceived in Great Britain is not itself unnecessarily large. The French have only three,

1 The Italians were about to introduce the four-gun battery in proportion as the Deport gun replaced the Krupp.