Both shoulders of this salient were to be attacked simultaneously, the Fifth Army operating on the Ancre, while the Third Army attacked from the north-west about Arras. Further, to quote from Sir Douglas Haig's despatch: "The front of the attack on the Arras side was to include the Vimy Ridge, possession of which I considered necessary to secure the left flank of the operations on the south bank of the Scarpe. The capture of this ridge, which was to be carried out by the First Army, also offered other important advantages. It would deprive the enemy of valuable observation, and give us a wide view of the plains stretching from the eastern foot of the ridge to Douai and beyond. Moreover, although it was evident that the enemy might by a timely withdrawal avoid a battle in the awkward salient still held by him between the Ancre and the Scarpe, no such withdrawal from his important Vimy Ridge position was likely." The rôle of the Highland Division was to capture the southern shoulder of the Vimy Ridge in conjunction with the Canadian Corps on the left and the 34th Division on the right. It was clear that an attack against a position of such great natural strength and tactical value as the Vimy Ridge would only be successful if the most careful and elaborate preparations were made. As far as the Highland Division was concerned, these preparations took three forms--the preparation of the British trenches for offensive operations, the preparation of the enemy's trenches for assault, the preparation of the troops for the attack. As regards the first much work was, as usual, necessary. The thaw, after a long period of intense frost, reduced the trenches to an appalling condition of mud. The overlay of loamy clay which covers the chalk in the Arras sector, when thoroughly wet, is of a bad texture for purposes of digging. It has such adhesive qualities that on many occasions during this period the earth could not be thrown off the shovel. The men working in the trench had to throw their shovels with their load of earth clear out of the trench, as had been the case in the Aveluy sector. Thus, the keeping open of the communication trenches and the opening up of the assembly trenches, which in any case were in a most desperate state of dilapidation, was a heavy task. As regards the preparation of assembly trenches, it was decided to form up the leading waves in the foremost old French trench. This trench had been evacuated owing to the danger from enemy mines when the Highland Division was holding this sector in 1916.