The town of Arras has a lot of ancient underground quarries, used during medieval times to extract limestone for building construction, and rediscovered during the war. These quarries gave safe haven to troops that would be used to break the German front line in April 1917.
The British High Command detailed officers of the NZ Tunnelling Coy to search for these old quarries in Arras in September 1916. Eventually, their efforts rewarded by the discovery of not one but several quarries under two major roads towards the front line, in the St Sauveur and Ronville neighbourhood, to the east of the town.
The discovery of these abandoned quarries gave birth to an ambitious plan for the British Army to break the German front line located just one kilometer to the east of Arras, in the early of April 1917. The British Army would concentrate a large number of troops without attracting the attention of the enemy and avoid the large scale slaughter experienced at Verdun and the Somme when troops massed prior to action. The plan would link these vast underground quarries with tunnels that would take the troops from the center of Arras to the German front line.
More than 500 men from across the British Empire were involved in the development of the Arras’ underground quarries. The British Army employed two sections of about 140 men of the 184th Royal Engineers Tunnelling Coy and all men of the NZ Tunnelling Coy to carry out this ambitious plan. Despite the large number of NZ Tunnellers, about 300 sappers, this was still under the number of men required to achieve their mission.
To the New Zealanders’ amusement, men of the 17th West Yorkshire Regiment, the 9th Scottish Rifles and the 6th King's Own Scottish Borderers strengthened the ranks of the Tunnellers at the end of November with the reward of an extra ration each day. The English and Scottish soldiers were impressed by the New Zealanders and made a pale impression beside them. Actually, most of them were Bantams, smaller soldiers than the average Tommy.
Experienced men in engineering works also joined the Tunnelers, along with 43 Māori of the Māori Pioneer Battalion arriving in Arras on 9th December 1916 under the command of the Lt Delautour. The next day the Māori got to work and leveled the soil quarries. Pākehā and Māori got closer very quickly and became friendly.
The beginning of November was cold and rainy. On 16th November 1917, snow fell for the first time that winter while the first section of the NZ Tunnelling Coy began working in the quarries of the Ronville system, located under the Arras - Bapaume road. The English Tunnellers began digging in the St Sauveur tunnel beneath the Arras - Cambrai road. Their first task was to open the underground quarries to the surface.
By the end of November, the company was strengthened by a reinforcement of new Sappers and was working actively. On 22nd November 1917, men dug a distance of 239 ft (72.84m) in one day: "the best to date" as stated in the war diary of NZ Tunnelling Coy. Each new days footage beat the previous days record. In one day alone, Tunnellers helped by explosives and a drilling machine, dug about 240 ft (73.15m) and the first galleries appeared.
As more men were employed on the project, widening of the tunnels increased considerably. During December footage records grew: 274 ft (83.5m) on 8th December, 289 ft (88.08m) the next day, 303 ft (92.35m) on 13th December. Finally, they established a new record on 16th December with 330 ft (100.58m) of new tunnel being driven.
Seven quarries were connected by 23rd December and work continued to connect the others. Works continued by setting up an electrical system to power and light the tunnels. Rock falls and collapses repeatedly occuried in the quarries at the beginning of January 1917. The Tunnellers leveled the quarries’ floors to for better stability and security.
Quarries connection was completed in mid-February and only the conversion remained to be done. In total, the St Sauveur system required the digging of 6 600 ft (2 012m) of tunnels and 7 500 ft (2 286m) for the Ronville system.
The entire system almost connected at the end of January 1917. The two main tunnels were the equivilent of a total distance of four kilometers. Work was not yet completed. The cellars of houses and some portion of the sewers, would have been connected to the two tunnels.
The Sappers used names of cities from New Zealand to name the quarries from the beginning of December 1916. Ronville system consisted of nine quarries called: Russell, Auckland, New Plymouth and Wellington symbolizing the North Island of New Zealand, and Nelson, Blenheim, Christchurch, Dunedin and Bluff, representing the South Island. These terms were simply the resumption of the name of New Zealand cities from the North to the South.
From 4th January 1917, the NZ Tunnelling Coy installed electrical wiring in Nelson cave and prepared installation of cables in tunnels and other quarries in order to bring light. Finally, on 24th February, the electrical system of the Ronville tunnel was switched on. Christchurch cave, the largest quarries, contained 248 bulbs while the smaller caves only have a dozen.
Since the beginning of March 1917, the men focused on digging tunnels under no man's land and in particular on the St Sauveur side. on 17th March 1917, the Germans withdrew to a location several miles behind the village of Beaurains. As the British advanced, the Ronville tunnel no longer took soldiers directly out in the German lines, but into the British rear lines.
Work continued in preparation for the big offensive on 9th April. At the end of the St Sauveur system, many tunnels, located in H and I sector, spread like the fingers of a hand and passed under no man's land until they reached first German front lines, while at the end of the Ronville system a single tunnel was constructed to allow the sending of reinforcements.
On the day of the offensive, the Tunnellers were confined to camp. Only a few Sappers were present to blow their mines, open the various tunnels to the surface and thus, allow to the British infantry to directly reach the German trenches.