On the 6th and 7th May the 152nd and 153rd Brigades went into the line, relieving the 10th and 12th Brigades of the 4th Canadian Division in the sector stretching from Bailleul on the right to Willerval on the left, the front line trenches being situated at the foot of the eastern slopes of the Vimy Ridge. The sector was well known to the older veterans of the Division, as it covered in its reserve area the greater part of the front held from March to July in 1916, and practically the whole of the front held in February and April 1917. On the right of the Division were the 15th (Scottish) Division and on the left the 52nd (Lowland) Division, so that on this occasion the line from the river Scarpe on the south almost up to Lens on the north was held by Scottish troops. The area occupied by the Division had been the scene of a great German attack on 28th March 1918. The 56th (London) Division had, however, offered a magnificent resistance, and apart from the loss of the foremost trenches held by their outposts had held their ground in spite of repeated attacks delivered by the Germans in great strength. The actual line taken over by the 51st Division as the front line had before the attack been the reserve line, or, rather, the front line of the reserve system. The whole scheme of defence had therefore to be recast so as to transform this reserve system into an outpost system and to create a new reserve system in rear. There was not the same amount of new work required as had been the case in the sector astride the Bapaume-Cambrai road, since numerous trenches and dug-outs existed which could be incorporated into the new scheme. As, however, the Division was now primarily composed of boys, who were unable to carry out a daily task equal to that of the old trained soldiers, the work contemplated was more than sufficient to keep the Division fully occupied for many months. In the new scheme of defence the system of holding a position by a series of trench lines was abandoned. The experience of the last two months had proved that the Germans were conducting their attacks in the main according to a stereotyped plan. This plan was to attack frontally with a great weight of artillery and trench-mortars on a narrow front, and thus blast open by an intense bombardment an area of penetration through which the attacking troops could pass and operate outwards against the flanks thus created. In this manner they had been able to roll up one trench line after another in a series of flank attacks. To meet this form of advance a trench system was planned which consisted of a number of localities, sited checkerwise, each locality being capable of all-round defence. Thus if the enemy penetrated any portion of the defences, whichever way he turned he would be met by entrenched troops facing the direction of his advance.