Junior officers and N.C.O.'s gradually acquired the necessary habit of true command over their men. The men were quick and ready to discover that the better disciplined a unit is, the more efficient it is, the less it suffers from the actions of the enemy and the conditions of war. They learnt, too, that the best-disciplined battalion is the most comfortable and the most contented. As Lord French writes: "Each unit learned by degrees its own relative place and position in the great Divisional machine. Enthusiasm was raised in the idea engendered in all ranks that they formed part of a great engine of war, furnished by their own country and immediate neighbourhood." In the early stages of its apprenticeship the Division first took part in a series of unsuccessful attacks. Subsequently it passed many weeks in areas in which trench-mortaring and mining--the two forms of trench warfare most trying to men's nerves--were considerably in evidence. Nevertheless, in spite of their inexperience and of this unfortunate beginning, the men at all times remained in good heart and retained a high standard of morale. By August 1915 the Division had so successfully overcome its earlier difficulties that it was selected to instruct the 18th Division, newly arrived from England, in trench warfare. Subsequently the 22nd Division, 32nd Division, and afterwards the 36th Division, were also attached to the Highland Division for tours of instruction in the line. Throughout this period the rivalry between the Territorial and New Army Divisions was acute. The men had a strong impression, further accentuated by the fact that the Division did not take part in the battle of Loos, that since they were a Territorial Division, the higher command would never employ them as a complete Division in a major operation. In this belief, after General Harper had taken over command of the Division, they began to call themselves Harper's Duds, asserting that the Divisional sign, H.D., was formed from the initial letters of these two words. On 27th July 1915, orders were issued by the Xth Corps for the 51st Division to take over the lines from near Becourt to the river Ancre near Hamel, relieving the 22nd Division of the XIth French Corps. On the night 30-31st the 152nd Brigade took over the left sector from the 116th French Regiment. On the following night the right sector was taken over by the 154th Infantry Brigade, who relieved the 22nd French Territorial Regiment, and by the 153rd Brigade, who took over a portion of the right sector from the 44th French Brigade. The Divisional artillery, with six batteries of the 18th Division attached for instruction, moved into the line in relief of the French artillery on the nights 2-3rd, 3-4th, 4-5th August.