Dhe Corps was rigid in adapting the Board of Directors to the battle...

The need to give the army corps a less rigid structure became apparent as soon as it came to conducting offensive actions. The two organic divisions were indeed insufficient to conduct attacks on a front and of sufficient depth: 3, 4, sometimes 5 divisions were considered necessary for an army corps.

In addition, for these operations, the Corps had to be reinforced by a large number of undivided units belonging to different arms, providing it with sufficient resources. From 1915, the composition of the corps was therefore made more flexible. It became variable and it was necessary to bring the means of command and support into line with the new needs that had just emerged.
It was in the wake of the lessons learned from the offensives of 1915 that H.Q.G. issued two documents that would modify the role and composition of the corps, while reinforcing this level as the unit in charge of leading the battle.
Firstly, the Instruction of 16 January 1916 on the aim and conditions of a comprehensive offensive marks the essential stage in the evolution of combat doctrine. It breaks definitively with the precepts of the 1913 Field Service Regulations and enshrines the principle of the battle conducted around the preparation of artillery. The offensives must be conceived as a series of successive attacks, each of which is limited in depth by the preparation capabilities of theThese attacks must follow one another at a rapid pace, so as to prevent the enemy from recovering and rallying its reserves. The surprise, corollary of the reduction of the duration of the preparation will have to be sought by the implementation of a density of artillery formations whose number will have to mitigate the duration of the preparation phase.
Secondly, by the Instruction of January 26, 1916 on the offensive combat of large units the division becomes the "attack unit" and it is up to its leader to combine the action of the infantry and the effects of artillery, while focusing on the search for intelligence. The army corps, whose importance is growing, is defined as "the combat unit"; it is at its level that the battle is now conducted and that continuity of direction of the engagement, essential to success, is ensured. In other words, the corps becomes the French army's manoeuvring pawn. As such, two types of C.A. will gradually emerge:
on the one hand, corps destined to become part of the armed forces, either in charge of an offensive planned in the short or medium term, or deployed in a zone of the front where operations remain active, mixed with the military, or in a zone of the front line where operations are still active.These army corps were then organised around four divisions (this quaternary structure allowed the corps commander to manoeuvre, while having reserves built up at his own level). It was this structure that would prevail in Verdun when Pétain took command there.
on the other hand, the corps assigned to the "guard" of the passive sectors of the front, particularly in Lorraine and the Vosges after 1916: these army corps are articulated around a binary structure of two divisions.
Thus, the divisional echelon is demoted to the rank of large contact combat execution unit and the corps is raised to that of manoeuvre echelon ensuring the cohesion of the unit.The divisional echelon is thus demoted to the rank of a large unit executing contact combat and the corps is raised to that of a manoeuvre echelon ensuring tactical and logistical coherence in the conduct of the battle, capable of marking an effort in space and time, in particular by balancing the effects of its organic support or reinforcement in favour of a given large subor unit. As for the army, it retains its initial function of designing and conducting an autonomous battle and a complete logistical echelon. As of the Battle of Verdun, this organisation will be applied, since Pétain will organise his action zone into grouping zones corresponding to the zones of engagement of the army corps at his disposal. It is significant to note that nothing is written any more about the brigade, which thus loses any tactical role and now corresponds only to a grouping - often temporary - of two regiments. This hierarchical level will soon disappear.⁸.

In the area of support, a certain form of decentralization was introduced in the general organization of the corps.
The divisions were each given their own support autonomy, thus relieving the corps in which they were assigned. The corps retained only :

(a) command bodies to coordinate the action of the divisional supports.

(b) implementing bodies providing strictly indispensable support to those of the endivisional elements which remained indissolubly linked to them.

In fact, if the defensive periods or phases of the campaign were marked by a complete upheaval of the order of battle within the corps, at least for all the operations of the campaign, the order of battle was completely disrupted.offensive rations, and especially in 1918, when the initiative of the operations could finally be resumed, the command sought to constitute the Armies with a certain number of corps, with their organic divisions.
In short, after having on the whole counted :

By the end of 1915:
12 Corps with 3 D.I.;
15 Corps with 2 D.I.;
23 independent divisions.

End of 1916:
2 Corps with 4 I.D.;
10 Corps with 3 D.I.;
15 Corps with 2 I.D.;
20 independent divisions

Mid-1917:
16 Corps at 4 D.I.;
17 Corps with 2 I.D. to keep the sectors quiet;
14 isolated D.I.

In 1918, the whole French army was aligned on 30 Corps with 3 D.I. and 15 independent D.I., thus returning to the initial principle of 1914 of the army corps having a fixed number of organic divisions.

The movement of ideas on this issue did not end with the armistice. The note of 3 April 1919 from the Marshal in command of the French armies, on the conduct of the Great Units, while confirming the evolution previously indicated, seems to return to a more flexible conception of the number of divisions within the army corps.

In this study, written by the 3rd Bureau of the H.Q.G. and which aims to take the lessons of the war at face value, the corps remains a Large Unit with variable composition, a command body whose means are sufficient to absorb many means of reinforcement. In its employment, it remains the unit of the battle, responsible for leading, coordinating and sustaining it, according to a long-term mission.

With regard to the number of divisions assigned to the corps, the recommended formula is particularly flexible, since it combines the advantages of an order of battle that is as invariable as possible, with the need to adapt the Board to its various missions.

It provides for the corps in two aspects:

• That of the organic corps, with a fixed composition, with 2 D.I. and the non endivisional elements (today we would say EOCA).

• That of the battle corps, reinforced by one or more diviand elements of different weapons.

The supplements necessary to transform the organic AC into a battle AC will be provided by the independent divisions and the general reserves.

II-2. Verdun, corps battle, led by an army...

According to current standards of engagement, and of course in a proportionate ratio of forces, the area of action of the Second Army of 1916 at Verdun, would correspond today toAccording to current standards of engagement, and obviously in a proportionate ratio of forces, the area of action of the II Army of 1916 in Verdun would correspond today to the engagement of a brigade (a GTIA on the right bank, a GTIA on the left bank, a GTIA in support, at the handle of the fan, on the side of Fort La Chaume, etc.).⁹and a brigade artillery, certainly reinforced, capable of beating up to the parallel of Montfaucon). In other words, roughly 5,000 men deployed and engaged in an area of action that is between twelve and fifteen kilometers of front and a maximum depth of eight kilometers. In 1916, on the same terrain, Pétain deployed five army corps, i.e. 350,000 men, against an equivalent and sometimes greater volume of Germans!

If the difference in scale is of the order of 1 to 70, on the other hand, the major effect of this current brigade commander would be strictly identical to Pétain's intention a century earlier: Banning the Froideterre crest.

- Souville - Tavannes, making an effort on Souville.

It is therefore interesting to look at this "battle of corps d'ar mées" from the double angle of the corps erected in groups, and of the "noria".

a) The army corps erected in groups

The keystone of the defence of Verdun would be a sub-division of its action zone into grouping zones, each corresponding to the action zone of an army corps. We find here the main idea expressed by the Instruction on the use of the Great Units, signed by Joffre the previous month, and which made the army corps the unit of the battle. Pétain was to organise two groups on the left bank of the Meuse, one straddling the cut, two on the north side of the right bank, one on the south side and the last facing south. This is how each corps commander received his mission, his limits and his means. From 26 February 8 a.m.¹⁰the Balfourier Group (20th Corps) is split in two. On the left, the Guillaumat Group (1st Corps) took charge, upstream of Charny, of both banks of the Meuse, in order to better coordinate the mutual support of the two banks of the coupure. On 1 March, the Alby Group (13th Corps) joined the Bazelaire Group (7th Corps) on the left bank and extended as far as the tip of the Bois d'Avaucourt. On 2 March, the Baret Group (14th Corps) interposed itself on the right bank to defend the Meuse coast against the Woëvre River.

General Léon Zeller reported in his Souvenirs how Pétain, having just taken command in the midst of the chaos of the battle, organised these groups himself11 :

"At about 9 a.m., the General, leaving the office that had just been assigned to him and which was separate from ours¹² through the first-floor landing quietly passed through the groups who were discussing and perorating with animation, but without order, neither in ideas nor in the distribution of work. His appearance alone had succeeded in bringing down the tuning fork of rumours that filled the room. Even paler than usual, not speaking to any of those who had deviated in his path, he beckoned to the colonel of Barescut with a sign, inviting him to come and see him.¹³ and myself¹⁴ to come to him, beside my work table, all three of us standing before a large wall map which I had just had assembled, and on which I had sketched the probable, but very uncertain, course of the front which our troops were defending. Taking a piece of charcoal from my table and summarizing his intentions, he said, "Five sectors. In each one a route of access...". He then traced, first in dotted lines, the axes of communication of these sectors, then in solid lines the limits which would compartmentalize the zone. He applied all his attention to this delicate adjustment, with the binoculars in his eyes to see all the details of the map ... and I can still see the line that was drawn on the map.I can still perceive the trembling lee of the charcoal held in his right hand, while his left hand erased from time to time the lines that he judged to be faulty and which he corrected immediately.

This work, in which all his application and experience was concentrated, lasted a few minutes, at the end of which he gave us the following language, which I think I can quote word for word: "Establish quickly the following order, very briefly in a few lines with a sketch: I take the command

- The army zone is divided into five sectors, the boundaries of which are as follows. In each sector, a chief takes absolute command of the troops currently in the area and is responsible for the defence - These chiefs are, from left to right, Bazelaire alone on the left bank - Then Guillaumat, Balfourier, Baret, Duchêne

- Then repeat the order given by the Commander-in-Chief: resist on the spot, no one ordering any retreat - It is up to you, the staff, to then propose to me any measure to restore order by re-establishing the organic links as soon as possible ...".

8 Also because of the manpower crisis of the following year, when the divisions were reduced from four to three regiments, i.e. nine battalions, this "ternary" organization made it possible to keep the same number of large units, and even to increase them.

9 The missions of these AITGs could be as follows:

• GTIA Left Bank: Prohibit the line of ground movement Rating 304 - Death Man - Cumières.

• GTIA Right Bank: Use the enemy between the Louvemont - Bois des Caures line, inclusive, and Côte de Froideterre - Fort de Vaux, inclusive.

• GTIA Fort de Chaume : EMD counterattack in favor of one or the other of the first echelon GTIA. Priority GTIA right bank.

10 Pétain took command on the 26th at 0000 hours.

11 General Léon Zeller, Souvenirs sur Foch et Pétain, presented and annotated by Colonel Claude Franc, Paris, Economica, 2018, p.138.

12 That of the 3rd Bureau.

13 Chief of Staff of the 2nd Army.

14 Lieutenant-Colonel Zeller, Deputy Chief of Staff.