Beneath the trench warfare of World War One existed an entirely separate war underground: battles in the mines and dugouts between the Great Powers. In 1914–17, the underground war was a product of static trench warfare, essential to survive it and part of both sides' attempts to overcome it. In the stagnant, troglodyte existence of trench warfare, military mining was a hidden world of heroism and terror in which hours of suspenseful listening were spent monitoring the steady picking of unseen opponents, edging quietly towards the enemy, and judging when to fire a charge. Break-ins to enemy mine galleries resulted in hand-to-hand fighting in the darkness.   We are joined by Simon Jones to discuss the ingenuity, claustrophobia and tactical importance of the underground war. He is the author of “The War Underground, 1914-1918: Tactics and Equipment.”