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 The opposing forces in the battle at Cambrai were the British 3rd Army commanded by General Sir Julian Byng, and the German 2nd Army under General von Der Marwitz. The operation was originally planned as a large scale raid using tanks, but under the C-in-Cs direction it became a major offensive with the objective of breaching the Hindenberg Line, capturing Cambrai, and using the Cavalry Corps to exploit a breakthrough to the Northeast. Three tank brigades were distributed to the six attacking infantry divisions on a front at seven miles. A total at 324 tanks took part in the initial assault at first light on 20 November. A feature of the tank tactics was the use of fascines (rolls of brushwood) which were carried on each tank and used to drop into the enemy trenches to provide crossing. The tanks followed a carefully rehearsed drill in crossing the trenches and engaging the German infantry with their machine guns, under a co-ordinated artillery barrage.
Initially all went according to plan and on the first day an advance of nearly four miles was achieved. The cavalry and reserve infantry however were unable to exploit the advantage gained, and the tank crews, without reserves, and exhausted by their efforts, were withdrawn from the forward positions. Meanwhile the Germans had been reinforcing the front, and on 30 November began a counter attack which regained most of the ground. Although the original hopes for the battle were not realised, Cambrai was to have a profound effect on the future development of land warfare. 20 November is celebrated every year by the Royal Tank Regiment as Cambrai Day. The Victoria Cross was awarded to Captain Richard Wain for conspicuous gallantry during the first day of the attack, the second VC to be awarded to the Tank Corps in the first World War.
Each tank brigade had three tanks equipped with wireless and one for laying telephone cable. Wireless communications from brigade HQ's to tank battalions were thus possible, and the envelope illustrates the Marconi equipment dismounted in a trench. Use of wireless was considerably inhibited by fear of enemy interception (the German Army was adept at this) and also because it could operate only when dismounted from the tank. The full use of wireless to control armoured units had to wait for the invention of radio telephone (R/T) in the 1930's.
The divisional sign illustrated is the 51st (Highland) Division whose tanks suffered severely from determined German artillery at Flesquieres. The badge shown is that at the Tank Corps, first worn in 1917. | 
