There was an “underground war” fought during WW I that was very much an Engineer War. This war was fought in the tunnels of both sides where the tunnelling tasks fell primarily to the Tunnelling Companies, Canadian Engineers.
During the war underground shelters and passageways were constructed in order to give our troops some protection from the violent confrontations occurring on the battlefield. Galleries were constructed off trench systems so troops could find shelter near the front. Tunnels allowed troops and supplies to move up to the front in relative safety and aided in the evacuation of the wounded. Tunnellers were also involved in offensive operations where a shaft would be driven under German front lines and loaded with explosives to be detonated in advance of an allied attack.
These tunnellers were not alone. The German Army was also engaged in underground operations and occasionally contact was made and pitched battles fought 100 feet underground. In the fall of 1916 a vast labyrinth of tunnels had been constructed by German, French, British, Australian, and Canadian Engineers along the western front. Mount Sorrel was a ridge held by the Allies against repeated German attacks.
On 16 September 1916, a troop of sappers of the 2nd Canadian Tunnelling Company was busy enlarging the tunnel system. Vibrations felt by the men indicated that there was an artillery battle going on overhead. The troop commander went to check the tunnel entrance for damage from shell fire. On emerging into the trenches he found German troops occupying the position. The half-mile long tunnels system was composed of narrow passageways that were just over a metre in height and included several exits. The Germans attacked the tunnels and suffered casualties as they were forced to advance through them in single file due to the constricted space. Despite the sappers having blown all but one exit, the Germans continued to infiltrate the system.
As any show of light attracted weapon fire, the battle was fought face-to-face in total darkness. The enemy was recognized by feeling for epaulets on the uniform - the Germans had them, the Canadian sappers did not. The sappers were equipped with knuckle- knives that were strapped to their wrists and made short work of any enemy they encountered. Casualties were heavy on both sides. When it seemed that all was lost for the sappers the Germans withdrew.
On the morning of the 17 September the tunnellers cautiously checked out the surface conditions. They were overjoyed to find British Tommies brewing tea. A counter attack during the night by the Allies had regained the position and the sappers could get back to their tunnelling work.