the hospital complex for destruction after receiving word that no additional information had been found by those combing the underground labyrinth. The charges were detonated at noon; after the explosion, large cracks could be seen on the surface for a distance of approximately two hundred meters. The team then moved to the second tunnel complex and, again using a combination of conventional demolitions and acetylene, destroyed it.

Because of the numerous enemy underground complexes discovered, there were too many burrows for the few trained tunnel rats to explore. Volunteers from the 1st Engineers and other units often took on the task of exploration and destruction. As would be expected, the results when using trained, experienced, and properly equipped personnel were much more valuable-and far safer -than those gained through volunteers. Unless the tunnel was mapped as it was explored, the engineers who were to destroy the tunnel were required to go back in and map it, duplicating effort. There were also instances in which two teams were in a tunnel at the same time with neither team knowing of the other's presence. Luckily, no one was shot by mistake.

A new method of tunnel destruction was developed and used during CEDAR FALLS. It consisted of filling a tunnel with acetylene gas-forced in by blowers-then igniting the gas by demolition charges. Acetylene alone was found excellent for destroying tunnels with not more than seven feet of overhead cover. With deeper tunnels destruction was increased through the use of conventional demolitions in conjunction with the acetylene. Thirty-pound charges of TNT and 40-pound cratering charges were placed at critical locations (rooms, tunnel junctions, exits, and entrances) in the complex. These charges were dual primed, connected in series by detonation cord, and fired electrically. When detonated, the conventional charges acted as booster charges for the acetylene. These experiments, using high explosives and acetylene together, proved very effective on tunnels as much as fifteen to twenty feet below the surface.

During Operation CEDAR FALLS the 1st Engineers and attached units discovered literally helicopter loads of documents, records, and plans, many of which belonged to the Viet Cong intelligence section of Military Region IV from 1963 through 1966. The documents listed the strengths of Viet Cong units, the names of their members, and the towns and villages in which they operated; disclosed some of their meeting places; and revealed a great amount of information on exactly how the enemy operated and what his future plans were. In addition to intelligence gathering and