Tunnel warfare

Tunnel warfare is a general name for war being conducted in tunnels and other underground cavities. It often includes the construction of underground facilities in order to attack or for defence and the use of existing natural caves and artificial underground facilities (catacombs, city communications, etc.) for military purposes. Tunnels can be used to undermine fortifications and slip into territory, while it can strengthen a defence by creating the possibility of ambush, counterattack and the ability to transfer troops from one portion of the battleground to another unseen and protected. Also, tunnels can serve as shelter for combatants and non-combatants from enemy attack.

It can be sometimes linked with urban warfare, as tunnels are often found in urban areas and cities, although urban warfare as a whole usually dominates any tunnel considerations.

Tunnels, due to their nature, restrict fields of fire and thus any troops in a tunnel usually only have a few areas exposed to fire or sight at any one particular time. Also they can be part of an extensive labyrinth and have cul-de-sacs as well as reduced lighting that can create a closed-in night environment.

Tunneling in order to mine enemy fortresses and make the walls crumble is an ancient military art that has been put in use all over the world. Polybius describes the Seleucids and Parthians employing tunnels and counter-tunnels during the siege of Sirynx. A famous mine made the walls of Kazan crumble, allowing the Russians to take it. The only countermeasure was to dig down, intercept the mine, and fight the advancing enemy soldiers underground. Sometimes the tunnels collapsed during the fighting, and both sides were buried alive.

...
Wikipedia