Military tunnels are often associated with covert explosions under enemy lines but the Wellington Quarry at Arras housed up to 20,000 Allied soldiers and a 700-bed hospital.
The 20km network of tunnels was built by the Royal Engineers, including Australians, and the New Zealand Engineers Tunnelling Company.
They were preparing for a major British offensive, the Battle of Arras, in April 1917.
Five-hundred miners worked for a year to forge the tunnels and connect them with existing mines dating back to mediaeval times.
Many of the men were called ‘Bantams’ because they were soldiers of below-average height who had been rejected by regular units. Others were deemed too old but their specialist experience made them invaluable to military mining.
The tunnels ran from the Arras town centre, under No Man’s Land, to points just in front of the Germans’ Hindenburg Line.
They were outfitted with running water, electric lights, kitchens, toilets, light rail and a fully equipped hospital. The network was so extensive that tunnels had to be named, and the New Zealanders honoured places from home.
Today, the tunnels are open to the public as Carrière Wellington – Memorial de la Bataille D’Arras, an underground museum managed by the Arras Tourist Office and dedicated to the British Army and its Dominion Forces, including Australians.
Visitors in groups of up to 20 are taken in a glass-sided elevator to 20m below ground level, then guided through the tunnels and remnants of the First World War occupation, including mining equipment, glass bottles, tins and rum jars.
The displays show the work of the miners, the military strategy used in construction, and the daily life of soldiers living underground.
There are also marks from 100 years ago when soldiers carved their names, directions and drawings into the walls.
At the end of the tour, visitors pass Exit Number 10 which was used by soldiers to climb up to the front line positions and go into the attack.
At 5.30am on 9 April 1917, exits were blasted and the Allies stormed enemy trenches.
The initial action was regarded as a success. The Germans were pushed back 11km and the Allies captured Vimy Ridge, north of Arras, but the offensive became bogged down and was called off as Allied casualties reached 4,000 a day.