Once the war lost its movement, Armies developed possibilities of attacking from underground using the age old tactic of military mining. Under no man's land, tunnellers dug long galleries towards the enemy front line with the aim of destroying his infrastructure from deep below ground.
With strategy as its main asset, the war underground was a difficult war to retain the top position on the table. The Tunnellers played a kind of mortal chess. They tried to be more crafty anticipating attacks of the enemy. Loud noises and movement caused by panic or lack of attention to detail brought the Sappers closer to death. The men had to be aware of the dangers they faced and adopt a safe and effective method of work. The detection of the enemy’s underground signature and noise influenced defensive digging as they tried to outflank him.
With luck, surface and aerial observation might give few indications of the entrance of enemy tunnels. Nonetheless, those observations could not show the extent of an underground system. The only way to locate the enemys underground activities was through the carefull and time consuming art of listening.
The men used listening instruments such as the geophone. This instrument was composed of two wood sensors, containing mercury between two mica diaphragms. The sensors were linked to a stethoscope. The operator moved the sensors on the floor, on the walls or on the ceiling of a gallery. He could hear suspect noises and with help of a compass, he obtained the orientation and distance of the sounds.
Noise discipline in your own galleries was paramount. The only way to communicate underground was sign language. Verbal communication was very risky and easily detectable by the enemy. In the beginning of March 1916, the New Zealand Engineers Tunnelling Company spent most of its time listening in its tunnels and galleries it had constructed. Listening in the chalk was very hard work, even the slightest noises out to 100 meters were easily detectable by geophone.
The men worked in shifts composed of an officer, a Sergeant, a Corporal, a Lance-Corporal and 15 Sappers. Infantrymen attached to the Tunnellers helped them as labour. Each shift worked 8 hours followed by 24 hours out of the line.
The NZ Tunnellers adopted their digging methods through personal experience rather than following what was laid down in Royal Engineer manuals. Whereas some Tunnelling Companies preferred using vertical shafts as a means to gain depth, these shafts were extremely vulnerable from enemy fire and they made the disposal of spoil from the galleries a very slow and laborious process. Once discovered a mine entrance was always followed by a constant bombardment.
The small tunnels made by the British, French or German Tunnellers did not appeal to the tall nature of the NZ Tunnellers. Other Tunnelling Companies used a typical size of 3 ft (0,91m) wide by 4 ft 6 inches (1,37m) high for their tunnels. The New Zealanders adopted a gallery of 6 ft 3 inches (1,90m) high by 3 ft 6 inches (1,06m) wide. With these dimensions, the NZ Tunnellers made better progress with infinitely more comfort whilst they swung their pick. Mine depth depended on the geology. Galleries were located normally between 5 meters and down to more than ten meters beneath the surface.
It took time to prepare the workings required to support an offensive mine. From 10th April 1916, the Tunnellers began works for a new gallery, designated J8. Tunnellers actively dug until the end of April. The enemy seemed very quiet and no activity was detected. The works progressed swiftly. Three new tunnels made. The next time German mining was detected in this location was the 21st April.
New Zealand and German activities increased every day. Each new gallery dug contributed to the New Zealand Tunnellers effort to drive back the Germans. The Germans effort in digging and maintaining their systems did not go without notice to the New Zealanders.
Once a German system had been located and identified the fight was on to destroy it. In the war underground, galleries were driven very close to enemy tunnels and trenches. The Tunnellers placed explosives at the end of a gallery in order to destroy an enemy position.
On 4th May 1916, the NZ Tunnellers charged galleries with explosives. Next day, the tunnels were prepared for firing at 10pm. The detonation of 4 camouflets passed without incident. However, as there was no post target reconnaissance they were unsure just how successful their counter mining had been. A few hours after the firing, the NZ Tunnellers cleaned their tunnels and started working again. Their blow seemed to be a success. The Germans were not heard in the vicinity their destroyed galleries. The only answer from the enemy was an intense bombardment of the British trenches on 7th May.
Until their involvment in the big scheme of the Arras’ underground quarries in November 1916, the NZ Tunnellers were engaged in the war underground against the enemy. When out of the line, they were billeted in the norther part of the front line around Arras. At work they showed a savage face in opposing the German mine threat.