<P> Communist forces deployed several countermeasures against the American tactics . Avoidance and concealment was a primary method - sometimes made more difficult by the "sniffer" technology . But chemical detection was not always reliable - and could be thrown off by the use of animal decoys, urine bucket diversions, or was affected by wind, rain and other factors . VC / NVA units also built their fortifications in the high brush along canal banks and streams - providing a route of easier escape from the American attack . These locations could be a double - edged sword: they gave clear fields of fire against American infantry but the adjacent rice paddies sometimes created convenient enemy landing zones, and the water escape routes could become bottlenecks . Pre-built fortifications and trenches helped shield the communist forces from annihilation as the ring closed in, and previously prepared ground, laced with booby - traps also delayed enemy forces . If there was enough advance warning, VC / NVA forces would prepare kill zones near or in likely landing spots . Trees could also make effective defensive positions . Booby traps were laid on trails and rice paddy dikes, and in jungle growth in a random pattern, and often caused multiple casualties to American troops . </P> <P> The primary tactic after being surrounded was to delay until nightfall, after which breakouts would begin . Large formations were broken down into smaller units to facilitate escape and a rendezvous was pre-planned in advance . Special units were deployed to probe the encirclement, looking for weak points, and decoy units were held ready for action to occupy American forces once the breakouts began . Breakouts could be made with diversions while bodies of troops slipped away, or strength could be concentrated on a weak spot, providing enough local superiority to penetrate the American encirclement and disperse . Escaping units would link up later at designated marshaling points . Harassment and diversionary tactics also paid dividends . As noted by some airpower historians, relatively small bodies of local fighters armed with inexpensive rifles, could divert and tie down expensive and massive allocations of men, material and time deployed by more sophisticated opponents . </P> <P> Ironically, the very efficiency and convenience of firebases, could at times aid VC / NVA forces . In some areas, US troops, often used as "bait" to draw out an enemy response, developed "firebase psychosis" - a reluctance to move too far away from the covering artillery of their firebases . As a result, combat movement and operational flexibility was hampered, and more mobile communist forces attacked, broke contact, maneuvered around and eluded their opponents . Many firebases were also totally dependent on helicopters for construction, resupply and evacuation, and communist attacks against these fortresses could at times force their abandonment . </P> <P> Main force confrontation . VC / NVA forces also faced American airmobile attacks in remoter areas, around their base camps and border sanctuaries . In these encounters NVA regulars and VC main - force units confronted their opponents, which sometimes included airlifted ARVN elements . Typically, such airmobile operations involved preparation of fire support bases, carved out of jungle terrain . Suitable areas (usually on high ground) were selected and heavily bombarded with artillery and airstrikes, then US engineers and security troops landed to commence construction of fortifications, bunkers, artillery emplacements and helicopter landing pads . The ability of helicopters to transport all the needed men and heavy equipment to almost any location gave American arms tremendous power and flexibility . Several of these firebases could be built relatively quickly and deliver devastating mutually supporting supporting fire within a combat zone . Under the artillery umbrella, Marine and army infantry deployed for combat . The versatility of helicopters enabled such forces to be resupplied and maneuvered to numerous points on the field of battle . Firebases could also be "leapfrogged" or shifted in response to an advance or operational needs . </P>

What was the vietcong war strategy in fighting american forces