At Cambrai the Tanks were on their trial. It was their special "show," and if they failed now they would fail for good. Their commander, General Elles, took no chances. With three brigades of Tanks he was to break through the enemy’s wire, cross the broad trenches of the Hindenburg Line, and open the way towards Cambrai for the two Army Corps following. The enemy defences were the strongest in the West. There were three trench lines, each of a width extending to 15 feet, and with an outpost line thrown forward as a screen. In front of the main line lay barbed wire at least 50 yards wide, which sometimes jutted out in bold salients flanked by machine-guns. It was calculated that to cut that wire with artillery would have taken five weeks and cost twenty millions of money. The trenches were too wide for an ordinary Tank, so immense bundles of brushwood were made up, which a Tank carried on its nose and dropped into the trench to make a crossing. Each bundle, or "fascine," weighed a ton and a half, and it took twenty Chinese coolies to roll one of them through the mud. The attack was to be a surprise, and therefore there was to be no preliminary bombardment. Secrecy was so vital, and the chances of discovery so numerous, that the commanders spent anxious days prior to the 20th November. Flotillas of Tanks were assembled in every possible place which afforded cover, notably in Havrincourt Wood. The Tank is not a noiseless machine, and it says much for the ingenuity of the Third Army that the enemy had no inkling of our business. A single enemy aeroplane over Havrincourt might have wrecked the plan. On the night of the 18th an enemy raid took some of our men prisoners, but they must have been very staunch, or the German Intelligence Service very obtuse, for little appears to have been learned from them. The weather favoured Sir Julian Byng. The days before the assault had the low grey skies and the clinging mists of late November. In the dark of the evening of the 19th the Tanks nosed their way from their lairs towards the point of departure, going across country, since the roads were crowded, and running dead slow to avoid noise. That evening General Hugh Elles issued a special order announcing that he proposed to lead the attack of the centre division in person, like an admiral in his flagship. At 4.30 on the morning of the 20th a burst of German fire suggested that the enemy had discovered the secret, but to the relief of the British commanders it died away, and the hour before the attack opened was dead quiet. [Illustration: Cambrai—the Advance of the Infantry Divisions on November 20.]