They were an underground army to themselves. Leading the way were soldiers known as “clay-kickers,” who leaned back on inclined boards and kicked spades into the heavy French soil, carving it out inch by inch. Following on their bootheels were the “moles,” who enlarged each cavity. Finally came munitions experts, who carefully packed the chambers with explosives. Together, the tunnelers toiled beneath the Western Front fields of Flanders.
At the outset of World War I in early August 1914 the Germans invaded Belgium and quickly pushed through to France. The Allies were able to halt their advance a month later at the First Battle of the Marne, after which the conflict settled into a disastrous stalemate that would claim millions of lives. Combined casualty estimates at First Marne alone approached a half-million. The combatant armies then dug in along a meandering line of fortified trenches stretching some 440 miles from the North Sea to the French-Swiss border.