The us army and the army of the Republic of Vietnam has constantly attacked the system of tunnels by sufficient means: bombs, pumping water into the tunnels, but selected by the system of tunnels are designed can isolate each part should be damaged. The us military has imposed several measures to detect the doors (disguise) and discovered the ventilator (usually placed between the bushes). The most effective measure is to use dogs. Initially some of the doors and vents were discovered by professional dog dogs smell slightly. However, after that, the people at the lower tunnels have used American SOAP set in the mouth of the tunnel and ventilation should not be professional dog discovered.
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