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.
The trench was reconnoitred throughout its length, and it was found to have fallen in to a depth of about four feet, and to have been completely filled in with entanglements of barbed wire. There was, further, a fairly strong wire entanglement in front of it. The saps connecting this trench to the present front-line trench had all been completely blocked when they joined the existing front line, and had also been wired up throughout their length. A large amount of work was therefore required to clear this trench so that the troops could occupy it for assembly. It was, however, decided to do no work in it beyond removing the barbed wire from it so as not to attract the enemy’s attention.
The whole area was found to be very deficient of dug-outs suitable for headquarters. Three new brigade battle headquarters had therefore to be tunnelled as well as some additional battalion battle headquarters and regimental aid posts.
Machine-gun positions had also to be constructed for guns firing in the machine-gun barrage during the attack, and accommodation had to be provided for their crews.
The Divisional area also contained an insufficiency of artillery positions, particularly of forward positions required by the guns firing in the barrage. Considerable preparations had therefore to be made by the artillery.
The system of buried telephone cables was also incomplete. In fact, it was only completed in time for the engagement by concentrating every available man on this work.
As regards the preparations of the enemy’s position for the attack, the chief consideration was his wire entanglements, which had been erected in profusion.
Those which were to be encountered in the first phase of the attack, being on the western slopes of the Vimy Ridge, were visible, and could be cut by the artillery with direct observation.