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undue expenditure of ammunition. The usual result was that the gunners retired a few hundred yards (if they had no deep dugouts) till the shelling was over, and then came back to their guns. If they were shelled again they shifted their guns to an- other position. The ground in front of Vimy Ridge was a mass of positions from which batteries had been shelled out, and it was reckoned that one position in four was occupied. The British and the French used to repair abandoned positions to encourage the enemy to go on shelling themr Flashes were fired from dummy positions for the same purpose. " Silent " positions, from which the guns were not allowed to open fire till active operations began, were rarely located.

The Germans were fairly successful in neutralizing batteries with gas shell; concealed artillery positions, being usually in hollows or woods, are specially vulnerable to gas attack. If such a position be thoroughly drenched with persistent gas it becomes untenable, since men cannot work in gas-masks for a prolonged period. In future, flashless powder will make it still more difficult to locate concealed artillery positions.

III. THE BREAK-THROUGH

During the three years 1915, 1916 and 1917 numerous at- tempts were made to break through the opposing line, the most notable being the German attack on Verdun. All these attempts failed; the less unsuccessful of them resulted merely in the cap- ture of an unimportant strip of ground at a heavy cost. A dis- cussion of the reasons for these failures would be beyond the limits of this article. From an artillery point of view it is more important to consider the method of attack which was finally evolved. The two leading principles are the following:

(a) Surprise. This implies the rapid and perfectly timed concentration of artillery and infantry units in the area of the attack, so that they arrive just when they are wanted. If, as is probable, the result of the attack is that the enemy's line is not broken, but is only bent back, successive surprise attacks are made by shifting the weight of the attack quickly to other

1 points which may be 50 or 100 m. distant, so as to form salients in the enemy's line, which are then " pinched out " by attacking them from both flanks. This, at least, is the obvious course; and, because it is so, it may not be the best one'. In some cases a commander may decide that he has a better prospect of sur- prising the enemy by renewing his attack on the original point. Success depends principally on an organization which enables guns and men in large numbers to be placed in readiness for ac- tion in any selected area of attack either without the enemy's knowledge, or so quickly that he has no time for counter- preparation.

(b) Wide Front. It is useless to make a narrow gap in the enemy's line, commanded by his guns from both sides. It must, roughly, be wide enough to allow for 10 m. of shelled ground on each side, and a 20 m. passage down the middle; that is, about 40 miles. The Germans in March 1918 attacked on a 50 m. front.

Concentration of Artillery. The first step is to prepare for the concentration on the front of attack of a sufficient number

of guns. Normally the line is held by about one gun to 30 yd., including field, medium and heavy. For an attack, this number must be at least trebled.

The Germans, in their great attack of March 1918 on the 50 m. front from Monchy to La Fere, had the following, counting normal establishments only:

I field gun per 19 yd. of front

I field howitzer per 57 yd. of front

I medium howitzer per 128 yd. of front

I heavy gun per 128 yd. of front

I heavy howitzer per 256 yd. of front

I superheavy howitzer per 512 yd. of front.

This alone amounts to one gun per 1 1 yd. of front ; but in addition to this the four-gun field batteries werereenforced, as far as possible, by adding two guns from reserve. The extra guns were not horsed and the gunners were provided from personnel on the spot. 1 There were also a certain number of miscellaneous guns and a very liberal equipment of trench ordnance. Altogether it may be estimated that the Germans, in this attack, had one gun per 9 yd. of the whole front attacked; but since the attack was pushed home only on alternate sections of this front the concentration of gun-fire on the real fronts of attack was much heavier than these figures imply, as explained below.

In the still more highly developed artillery attack of May 27 1918 on the Chemin des Dames the strength (according to Col. Bruch- miiller, who was responsible for the arrangements) was

I field gun per 26 yd. of front (not including about 30 batteries

told off as accompanying artillery), field howitzer per 47 yd. of front, medium howitzer per 99 yd. of front, heavy howitzer per 156 yd. of front, medium or heavy gun per 200 yd. of front, superheavy gun or howitzer per 1,126 yd. of front, or I field piece per 17 yd. and

I medium or heavy or superheavy piece per 49 yd.

In the aggregate I piece per 12 yd. irrespective altogether of accom- panying artillery, additional guns, and trench mortars.

In the battle of July 15 1918 the last German offensive the trench-mortar strength was approximately one per 30 yd. for a con- siderable frontage, and locally as much as one per 10 or 12 yd.

Positions for Artillery. Assuming that, for an attack, the artillery of a front, normally one gun per 30 yd., has to be in- creased to one gun per 10 yd., positions have to be prepared for the reenforcing guns. A certain number of spare positions with gun emplacements protected by overhead cover will already exist as part of the equipment of the front, but it is rarely possible to provide labour on such a scale that a defensive front is always kept ready to be used as an attacking front.

If it be possible to bring up the whole of the reenforcing guns during the last night before the attack the preparation will con- sist principally of marking out gun positions and roads to them, and laying telephone cables to them and to the observing posi- tions. But even with motor equipment the concentration of the whole movement of the troops into one night imposes such a strain upon the transport that it will usually be necessary to spread the movement over three nights, and in this case efficient camouflage must be provided for the guns which arrive before the last night.

1 They were intended only to take part in the bombardment and not in the advance which followed.

The following table, from the Revue d'Artillerie of May 1921, shows the densities of artillery strength in certain French battles of

Yards of front per gun.

i field gun per

I medium or heavy gun per

I medium or heavy howitzer* per

I medium or heavy gun or howitzer per

"1

I super- heavy piece per

Champagne, Sept. 25 1915 Somme, July I 1916 .... Aisne, April 16 1917 .... Verdun (Mort-Homme battle) Aug. 20 1917 Malmaison, Oct. 23 19^7.

36yd. 36 !!

22 " 2O "

18 "

66yd. 50 " 45 "

133 yd.

68 " 59 "

44Xd. 29 " 26 "

121 yd.

255 "

The French had no field howitzers.

The French " Offensive Instructions " of Oct. 31 1917 lay down a scale for the first-class offensive battle of about I field gun per 15 yd. I medium or heavy piece for demolitions per 30 yd.

I " counter-battery per 35 yd.

Superheavy pieces approximately at I per 170 yd. (pi

for tank action).

us i piece of trench ordnance per 30 yd., except in parts of the front reserved