Tunnel warfare is a type of warfare that occurs in tunnels. It can be sometimes linke with urban warfare, as tunnels are often found in urban area and cities, although urban warfare as a whole usually dominates any tunnel considerations. Tunnels can be used to undermine fortifications and slip into territory, while it can strengthen a defense by creating the possibility of ambush, counterattack and the ability to transfer troops from one portion of the battleground to another unseen and protected.