One brigade of artillery covered each battalion front, while the 3rd Brigade of artillery covered its whole infantry brigade front. The fifteen 18-pounder batteries firing in the creeping barrage fired 33 per cent of smoke shells, so as to screen the movement of the tanks. Two 4·5 howitzer batteries also kept a standing smoke barrage in front of Flesquières Ridge. No registration was carried out, so that the presence of fresh batteries in the area might not be disclosed. The whole of the firing was therefore carried out from the map and by calibration. The concentration of artillery, tanks, and infantry immediately behind the line from which the attack was to be launched was successfully effected between 17th and 19th November with great rapidity and complete secrecy, mainly under cover of darkness. The artillery was moved up on 17th November; the tanks were assembled on the night of 18th November in Havrincourt Wood, and travelled to their assembly positions in the early hours of the 20th. The infantry came into Metz on the evening of the 18th, and began taking over the line on the 19th. It must be borne in mind that a similar concentration of tanks, guns, and troops was taking place simultaneously on the fronts of Divisions on either flank. The fact that all the necessary moves took place, and that the troops were eventually formed up in the assembly trenches without any suspicions being aroused in the mind of the enemy, shows how admirably the arrangements for ensuring secrecy were carried out. A taped line was laid out in front of the assembly trenches to ensure that the main wave of tanks formed up on its proper alignment. By zero hour the bulk of them were on this line, while the remainder which had been delayed from one cause and another were crossing the British front line. The twelve "Rovers" were formed up beyond this line, the third wave being deployed behind the support line. The platoons to form the first two waves in the attack took over the line on the morning of the 19th, and thus had an opportunity of viewing the ground to their front. At midnight the remainder of the four leading battalions arrived in their assembly trenches. Before zero hour the four battalions for the later stages of the initial attack were assembled in rear of the trench area, with their leading platoons on the Charing Cross-Trescault road. As soon as darkness set in the platoons which had arrived first set to work to make causeways across their trenches for the passage of the tanks. They also freed the troops that were to assemble during the night from any chances of confusion and unnecessary fatigue by placing in position red lamps, flags, signboards, and markers to show routes and positions of platoons. Before zero hour all ranks were issued with a hot meal.