An attempt was made to blow an assembly trench for the troops detailed for the attack on the Green line by means of tubes of ammonal buried in a shallow trench cut through the surface of the soil. The ammonal was discharged successfully, but the results were disappointing. The disintegrations in the soil caused by the explosion, coupled with the rain, produced conditions of mud that rendered the trench which the explosion had created impassable. During the fortnight preceding the attack patrolling and raiding were carried out with great activity, both with a view to gauging the strength of the resistance likely to be encountered and to inspect and damage the enemy's wire. This activity disclosed the fact that the German was employing knife-rests[5] made either of heavy timber or of iron, to fill the gaps caused by our artillery and trench-mortars in his entanglements. Knife-rests are not easily damaged by shrapnel sufficiently to give the infantry a free passage through them. Efforts were therefore made to locate the places where they were in use, and to destroy them with 4·5 howitzers. The fire of enfilade machine and Lewis guns was then employed to prevent fresh knife-rests being put in position to replace those which had been damaged. Twenty thousand rounds of S.A.A. were frequently fired in a single night for this purpose. At the end of October it was realised that these knife-rests were being employed by the enemy in most formidable numbers, and were becoming a serious proposition. A number of Bangalore torpedoes were therefore made and carried up to the trenches. Raiding parties then carried these torpedoes into No Man's Land with them, and blew gaps in the rows of knife-rests. On 1st November a particularly good raid of this nature was carried out. Lieutenants Booth and Carnie of the 6th Gordon Highlanders with a party of men placed four torpedoes under the enemy knife-rests. These were exploded, and after a short interval the officers led the party through the gap caused by the explosions. They then exploded four more torpedoes under the next double rows of knife-rests. The party returned without a casualty, and reported that still a third row of knife-rests existed beyond the last one they had damaged. Raiding parties had also been employed to enter the enemy's trenches to gain identifications--that is, to return with evidence as to what units were holding the line in front of the Division.[6]