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Previous: 3-141: Mountainous Terrain
3-143. Tunnel and complexes may be interconnected with other tunnels and caves, concealed by trapdoors or blocked dirt passages that are up to three or four feet thick. Secret passages are usually known only to selected personnel and are used mainly in emergencies. Tunnels and caves may be interconnected by much longer passages through which relatively large bodies of men may be transferred from one area to another. The connectivity of these systems often allows the enemy to move unnoticed from one area to another, eluding friendly forces.
3-144. Characteristic of a typical tunnel or cave complex is normally superb camouflage, conceal entrances, exits and camouflage bunkers. Within the tunnel and cave complex itself, side tunnels may be concealed, trapdoors are often hidden and dead-end tunnels or caves are used to confuse the attackers. Airshafts are usually spaced at intervals throughout a tunnel or cave system. In many instances, the first indication of a tunnel or cave complex comes from direct fire received from a concealed bunker. Spoils from the tunnel or cave system may be distributed over a wide area, giving clues to its existence. (Refer to ATTP 3-21.50 for more information.)
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