The sector was also honeycombed with mines from end to end, the enemy apparently being complete masters of the mining situation. In fact, his supremacy in mining had become so complete that, immediately prior to the relief, the French had drawn up a scheme for evacuating the front line except for lightly-held outposts. The plan they had intended to adopt was to recast the scheme of defence and construct amidst the existing network of derelict trenches a new support and reserve line. The scheme had been completed, and was on the point of being put into execution when the Highland Division took over the sector. The Divisional commander decided to continue with this policy. The construction of the new scheme of defences necessitated a vast amount of work, and was only fairly complete three months later when the Division left the sector. This alteration in the siting of the trenches demanded the construction of an enormous number of dug-outs. It soon became evident that without these the daily casualty list must be heavy. Not only was the artillery activity considerable, but the German had also concentrated in this sector every type of trench-mortar which had been evolved, and was extremely free in his use of them. The mining was of a more savage nature than had been the case in La Boisselle, and in many instances resulted in serious infantry fighting. The mines were, as a rule, blown by the enemy with two objects. If the breadth of No Man's Land was not considerable, they were frequently blown with a view to destroying our trenches with their garrisons. If, however, the breadth of No Man's Land was great, or his system of defensive galleries were good, he would blow his mines in No Man's Land with a view to occupying them as a line of observation and snipers' posts. By the frequent blowing of this type of mine, he was able to cover his front with a screen of craters which denied the British observation of his front line, and created for him a chain of commanding mounds along our front.