British troops in a captured secondary trench, Cambrai, November, 1917. The Battle of Cambrai (November 20 - December 7 1917) was a British campaign of WWI. Cambrai was a key supply point for the German Siegfried Stellung (part of the Hindenburg Line) and the nearby Bourlon Ridge would be an excellent gain from which to threaten the rear of the German line to the north. The operation was to include an experimental artillery action. The battle was largely an artillery-infantry engagement that achieved surprise and technical superiority against strong fortifications but weak German infantry and artillery defenses, which were quickly reinforced. The British attack demonstrated that the Hindenburg Line could be penetrated.