Members of the Tank Corps describe the excitement and rapid gains of the first day of the Battle of Cambrai, where new tactics and new technology helped the British to achieve that most elusive of advantages: surprise. After the mud-choked misery of Passchendaele, Cambrai was the first sign that an end to the stalemate of trench warfare was possible, and proved that the British could break through the strongest of defences - the German Hindenburg line. With Dan Snow.