General Sir Currie therefore decided to add a third company of four batteries to each battalion of the Canadian Machine-Gun Corps, thus bringing up to ninety-six the number of machine guns in each Canadian division. This entailed an increase in personnel of approximately 50 per cent of the strength of each machine-gun battalion. These companies were formed provisionally on April 12, 1918, by withdrawing fifty men from each infantry battalion. Of these men a portion was sent to the Machine-Gun Battalion to be combined with the trained personnel, so that each machine-gun crew would include at least four trained gunners. The remainder of the infantry personnel withdrawn as above stated was sent to a special machine-gun depot formed for the purpose, and there underwent an abridged but intensive course of training. Thus an immediate supply of reenforcements was insured. Twenty-three-ton lorries had been borrowed from General Headquarters to supply a modicum of transport to the new units, and on April 13, 1918, some of the new machine-gun batteries were already in the line at critical points. Sufficient troops were not now available to garrison the local defenses of Vimy Ridge, or to reenforce parts of the front if the enemy was successful in effecting a deep penetration. Two special brigades were therefore organized: The Hughes Brigade--Commanded by Lieutenant Colonel H. T. Hughes. Approximate strength, officers, 184; other ranks, 4,050. McPhail's Brigade--Commanded by Lieutenant Colonel A. McPhail. Approximate strength, officers, 148; other ranks, 4,628. Two companies of the Eleventh Tank Battalion (twenty-four tanks) were placed at the disposal of the Canadian Corps on April 13, 1918. These tanks had officers, drivers, and armament, but no other personnel. A sufficient number of trained Lewis gunners were found from the First, Third, and Fourth Canadian Divisional wings and the Canadian Field Artillery supplied the required number of gunners. The tanks were then distributed at the critical points in the corps area, namely: Behind the St. Catherine switch at intervals of about 300 yards, facing south--18 tanks. In the gap between the Souchez River and Bois-en-Hache, facing east--three tanks. On the ridge line behind Angres, facing east--three tanks. It was intended that these tanks should form points of resistance to check any forward flow of hostile forces and so give time to the Canadian infantry to re-form in case they should be forced back. In any event the tanks were to remain in action for twelve hours after coming in contact with the enemy and thus gain the time so essential in a crisis. The First Canadian Motor Machine-Gun Brigade, now returned from the Amiens Battle, was held as a mobile reserve at one hour's notice. Bridges, railways, roads, and pumping stations were prepared for demolition, to be blown up as a last resort.