Meanwhile, during the first three months of 1917, negotiations
of fundamental importance were proceeding between the high
commands and the Governments of France and Great Britain,
touching on the principle of unity of command. General
Nivelle desired to secure the command of all the forces involved,
both British and French. Certain differences of opinion early
declared themselves between the British and French com-
manders-in-chief. These were chiefly in the first instance in
connexion with the date of attack, and the extent to which the
French troops in front line should be relieved. The transporta-
tion service and the Nord railway were not equal to the work of
operations on so great a scale at so early a date as that proposed
by Nivelle; and in view of the fact that the British commander-
in-chief desired to give his troops some rest and training and was
somewhat sceptical as to the degree of success which would be
attained by the French, was desirous of limiting the extension
of his front to the Amiens- Villers Bretonneux road. A temporary
agreement on Jan. i that the attack should take place as early
as possible, and that the French should be relieved as far as the
above road by the end of Jan., did not satisfy Gen. Nivelle;
the latter referred the whole question to his Government and,
indirectly, to the British War Cabinet, with the result that a
Cabinet meeting was held in London on Jan. 15 at which both
Sir D. Haig and Gen. Nivelle were present. The conclusions
arrived at were as follows: (a) the British to relieve the French
forces as far S. as the Amiens-Roye road, relief to be completed
by March i; (b) the offensive to commence on April i at latest;
(c) vigorous exploitation to be undertaken by all the forces
both French and British, if necessary. The French troops in
front line were accordingly relieved to the Amiens-Roye road,
and preparations pushed forward to deliver the attack at the
earliest possible date. But the transport difficulties had become
so acute that, notwithstanding the fact that every available
British soldier was utilized for railway construction and other
work, a serious breakdown in the Nord railway system appeared
to be inevitable, and the matter had to be referred to the French
Government with a view to obtaining greater facilities. Further
negotiations in regard to the problem of command took place
secretly between the British and French Governments, and
materialized in the Calais conference on Feb. 26 and 27 1917.
This conference had originally been summoned to discuss the
question of transportation. There were present: M. Briand
(premier), Gen. Lyautey (Minister of War), Gen. Nivelle
(French C.-in-C.), Mr. Lloyd George (British Prime Minister),
Gen. Robertson (Cl.G.S.), Sir D. Haig (British C.-in-C.), Gen.
Kiggell (C.G.S.). A scheme was set before the conference by
the French Government for the establishment of an Allied
G.H.Q. and the appointment of a French generalissimo, and
the breaking up of the British divisions to form an "amalgam"
with the French troops. General Robertson and Sir D. Haig
were in complete ignorance of this proposal until the cut-and-
dried scheme was produced; the British Prime Minister, however,
while opposing the French proposal to break up the British
army and form an " amalgam " with French brigades, directed
these two officers to draw up a scheme of command, by which the
control of operations in the coming battle would be solely in
Gen. Nivelle's hands, and the British army under his orders.
This was the decision of the War Cabinet. The scheme was
accordingly drawn up in the course of the morning of Tuesday
Feb. 27, so that when the conference met at 11:30 A.M. on that
day, discussion was limited to questions of detail. Finally the
French War Committee and British War Cabinet agreed to the
following arrangements:
(1) The British War Cabinet recognizes that the general direction of the campaign should be in the hands of the French commander- in-chief.
(2) The British commander-in-chief to conform his plans to those of the French during the preparation and progress of the projected campaign.
(3) Within the limits of (2) the British commander-in-chief will be permitted to utilize his own resources and forces in the manner which he considers most desirable.
(4) In regard to (2) an exception will be made in a case where he considers that such action would endanger the safety of the army
or prejudice its success; in that case a report shall be made, together with the reasons, for the information of the War Cabinet.
(5) The respective Governments will decide the date at which the operations referred to in (i) and (2) shall be deemed to be at an end.
As all students of war agree, within the army of a combatant nation, unity of control is essential to secure the most effective execution of military operations. In theory, it is equally desirable in all circumstances. There is, however, a difficulty inherent in applying the principle of unity of control to Allied nations. This difficulty lies in the incidence of responsibility. For example, if the British armies are placed under the command of a French general, the British commander cannot be held responsible to the nation. The responsibility for the British armies cannot devolve on the French commander, and must therefore de- volve on the British Government. At the Calais conference, however, an effort was made by the British War Cabinet to make the field-marshal commanding the British forces retain responsibility by instructing him to conform his preparations to the views of the French commander, except in so far as he considered that this would endanger the safety of the army or prejudice the success of its operations.
The battle of Arras was the first occasion on which the experiment was tried of securing a form of unity of command, and after the conference of Calais the British forces to be engaged in the battle were placed, within the limitations noted above, under the general control of Nivelle. Certain differences of opinion, however, still existed, and the whole question was again referred to the Governments, with the result that the two commanders-in-chief and two Cabinets met in London on March 13 in order to define the position more clearly.
During the month of March, as previously narrated, the Germans continued to withdraw to the already prepared Hindenburg Line, followed up and pressed by British troops, until early in April they were established in positions covering that line. On the British side, the extensive preparations necessary were pushed ahead as quickly as possible and so far as the available transport facilities permitted. The general plan agreed upon was that the British attack should be launched as early as possible in April and that the French main attack on the Aisne should follow two or three days later. This was to permit and induce the German reserves to be drawn into the British battle and towards the British front, and thus enable the main attack by the French to be delivered with greater prospects of success and exploitation. The British actually launched their assault on April 9, but for reasons of unfavourable weather the French postponed their attack until April 16. Prior to the offensive the new German lines of defence on the British front ran in a general north-westerly direction from St. Quentin to the village of Tilloy-les-Mofflaines just S.E. of Arras. Thence the German original trench systems continued northwards across the valley of the Scarpe to the Vimy ridge which, rising to a height of 475 ft., dominates the country eastwards. The front attacked by the III. and I. Armies on the morning of April 9 extended from just N. of the village of Croisilles, S.E. of Arras, to just S. of Givenchy-en-Gohelle at the ncrthern foot of the Vimy ridge, a front of nearly 15 miles. The enemy's defences comprised the normal powerful defensive front consisting of three separate and heavily wired trench systems, and in addition, from 3 to 5 m. further E. a new defensive system, known as the Drocourt-Queant line, which in fact was a northward extension of the Hindenburg Line, branching from that line at Queant.
The great strength of these defences demanded very thorough artillery preparation, and this in turn could only be carried out effectively with the aid of the air service. A greater mass of artillery, both guns and howitzers, was used for preparation in proportion to the front engaged than had yet been available in any previous British attack. Three weeks prior to the attack the systematic cutting of the enemy's wire was commenced, while the heavy artillery searched the enemy's back areas and communications. Night firing, wire cutting and bombardment of hostile trenches, strong points and billets continued steadily
