Tunnel Exploration and Destruction

Enemy combat units generally did not use tunnel systems. Rather, as do most military forces, they relied on fighting positions, trenches, and bunkers for protection. Tunnel systems were dug by those relatively stationary Viet Cong elements such as village and hamlet cadres, logistical units, and headquarters elements. Consequently, tunnels were most often found in the enemy-controlled villages and logistical base areas but not necessarily in combat unit base camps.

Interrogated prisoners and returnees revealed that as a rule personnel of organized Viet Cong combat units did not know the location of such tunnels. They might frequently reveal the general location, but information to locate the tunnels precisely had to come usually from local cadres and rear service personnel.

Extensive tunnel systems were found throughout the Iron Triangle- Thanh Dien forest area. Operation CEDAR FALLS demonstrated that patience is the primary weapon to use against an enemy hiding in tunnels: wait for him to run out of supplies or to get curious about where you are or what you are doing. It was some times necessary to flush the enemy out with tunnel rats or riot control agents or to seal and destroy the tunnels.

Tunnel Rat Teams

A tunnel rat team usually consisted of from six to ten men led by an officer or a noncommissioned officer. The individual in charge had the responsibility of drawing a sketch of the underground complex from information relayed from the team members within the tunnel.

The lead element of the tunnel rat team was usually armed with a pistol equipped with a silencer (to fire in a tunnel without a silencer was to risk broken eardrums), hand telephone or "skull mike," flashlight, compass, and probe. One of the major problems in tunnel reconnaissance was that of communications. The skull mike (a transmitter strapped to the back of the skull) often became inoperative after a short period. In addition, the heavier U.S. communications wire which had to be used in lieu of the scarce lightweight Canadian assault wire added considerable weight and bulk to the team.

Lack of fresh air was also a problem for the men when deep in the tunnels. The "Mighty Mite" (an air compressor with blower) or an auxiliary helicopter engine rigged with a 50 to 100 foot length of hose was often employed to force fresh air into the tunnel systems.

The job of a tunnel rat was difficult at best. Hot, dirty, and gasping for breath, he squeezed his body through narrow and shallow openings on all fours, never knowing whether the tunnel might collapse behind him or what he might find ahead around the next turn, and sensing the jolt of adrenalin at every sound. Surely this modern combat spelunker is a special breed.

Description of a Tunnel Operation

The following is a description of the search and destruction of a large tunnel complex located in the triangle approximately six kilometers south of Rach Bap and about six hundred meters to the east of Route 14.

On 21 January a Viet Cong sympathizer was apprehended by the 168th Engineers and admitted having helped dig the underground complex. A patrol was organized from the staff sections of the 1st Engineer Battalion and was led by the sympathizer to the tunnel area where he pointed out several air holes and firing ports. Further examination of the area uncovered a base camp with several tunnel entrances.

The next day, after posting security forces, a thorough search of the tunnels was begun by engineer tunnel rats with initial negative results. Then a breather hole was blown open revealing the entrance to hundreds of meters of additional tunnel. About six hundred meters into the tunnel the engineers ran into an accumulation of CS, and the exploration stopped. The many documents found in the complex were taken to the G-2 of the 1st Division; upon evaluation of the papers, the G-2 determined that the search of the tunnel complex should be continued.

Next day the engineer tunnel rats returned accompanied by their counterparts from the attached chemical platoon. After exploring an additional 800 meters of tunnel, they found and removed a trapdoor, disclosing additional chambers and documents. Over one kilometer of tunnel had now been uncovered. Further exploration revealed an exit leading to another enemy base camp.

The exploration continued the following day, and more documents were uncovered and evacuated. As the tunnel rats crawled through the complex, they heard enemy voices. A CS grenade thrown by the team flushed five Viet Cong from the tunnel; they were captured as they scrambled out. Above ground; the security elements found a former hospital base camp complex 300 meters north of the camp discovered the previous day, and an investigation of tunnels of this complex was begun.

Early the next morning, the fourth day of exploration, the tunnel rats returned to the former hospital complex. Five huts were unearthed, each dug into the ground so that the roof was at ground level. Medical textbooks and notebooks, small quantities of medicine, and medical instruments were discovered in the 300 meters of rooms and chambers. The tunnel team returned to the second tunnel complex where the Viet Cong had been flushed, but CS in the tunnel prevented further exploration. Tunnel destruction personnel from the 168th Engineers arrived that afternoon and remained at the overnight position.

On 26 January, the day CEDAR FALLS terminated, the tunnel destruction team left for the former hospital complex and the exploration team returned to the "CS tunnel" complex. Using conventional demolitions and acetylene equipment, the team rigged 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.

New Methodology

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.

Results

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 jungle destruction, 9,445 meters of enemy tunnels, 4 villages, 27 base camps, 60 miscellaneous bunkers, and other facilities were destroyed by the engineers.