Previous: 3-136: Urban Terrain
3-138. The enemy will likely use tunnels and may have the advantage of marked routes and detailed reconnaissance. Because he is able to select ambush positions and withdrawal routes, the defender typically has the element of surprise. A defended position in an underground facility can be very effective in countering enemy subterranean operations. The best underground defensive positions are well protected and canalize the enemy into a killing zone to inflict maximum casualties.
3-139. When moving through tunnels, take great care to avoid booby traps. These are normally deployed near junctions and are often operated by tripwires. Standing water in tunnels provides excellent camouflage for antipersonnel mines and booby traps scattered on likely routes. With the battle above continuing, flooding and cave-ins are highly possible due to the likelihood of artillery barrages and the use of demolitions. Thus, identifying escape routes is essential.
3-140. Chemical defense is a constant concern for Soldiers conducting subterranean operations. In tunnels, Soldiers may encounter chemical warfare agents as well as industrial chemicals in dense concentrations. A chemical agent alarm system, carried by the point man, provides instantaneous warning of the presence of chemical warfare agents. M8 and M9 detection papers also test for the presence of chemical agents. (Refer to ATTP 3-06.11 for more information.)