In February 1916 further changes took place; the 4th and 5th Black Watch were posted to General Headquarters, and the 4th Camerons to the Base. These three battalions were replaced in the 154th Infantry Brigade by the 9th Royal Scots, the 4th Gordon Highlanders, and the 7th Argyll and Sutherland Highlanders. All the battalions in the reconstituted 154th Infantry Brigade had landed in France some months before the remainder of the Division, being posted to various regular brigades as an additional battalion. Thus, as regards the infantry, the original composition of the Highland Division was restored, with the exception of the 4th Cameron Highlanders, the 6th Gordon Highlanders, and the 9th Argyll and Sutherland Highlanders. During the same month changes were also made as regards the organisation of machine-guns. The infantry battalions had joined the Expeditionary Force each equipped with two machine-guns under the command of the battalion machine-gun officer. In July 1915 the battalion machine-gun section was increased by an additional two guns. In January 1916 a machine-gun company of sixteen guns was affiliated to each brigade. These companies were formed by the amalgamation of the four battalion machine-gun sections in each brigade, Captains Hardie, Calder, and Board commanding the companies of the 152nd, 153rd, and 154th Infantry Brigades respectively. In the early part of 1916 the trench-mortar situation was greatly improved. Three 2-inch trench-mortar batteries were formed by the Divisional artillery. These mortars fired the 60-pound bomb already described known as the "Donald Dinnie." They were still considerably inferior to the German trench-mortars in range, but they constituted a considerable advance on all previous experiments. Their chief faults lay in their liability to misfire, and in their frequent inaccuracy, due to the boxes containing the component parts not being water-tight. When the "Donald Dinnie" did burst on its target, the effect was gratifying. The retaliation they almost invariably drew from the enemy was the best evidence of their efficacy, and made the duty of serving the mortars an extremely hazardous one. In May 1916 a light trench-mortar battery, consisting of four Stokes mortars, was formed for each brigade. The Stokes gun proved the most satisfactory British light trench-mortar invented, and remained the weapon of the light trench-mortar batteries throughout the war. On 1st March 1916 orders were received for the Division to march northwards and take over from the 23rd French Division of the XII^{me} Corps d'Armée in a sector north of Arras, now known to history as the Labyrinth. This move was due to the necessity for the British to take over more line from the French. The object was to free as many French Divisions as possible for the defence of Verdun, against which the German was delivering his great attack.