CHAPTER VI

Engineer and Chemical Operations

Starting with the construction of the D. S. [double-single] Bailey Bridge at Ben Cat on 21 Dec 66, and ending with the demolition of the tunnel complexes on 26 Jan 67, Operation Cedar Falls was without exception the most significant combat engineering operation of the war to date. New concepts of jungle warfare using dozers to open heretofore inviolable VC strongholds; the emergence of a new "Secret Weapon," the dozer infantry teams; and combined acetylene and HE (High Explosive) tunnel demolitions; all have proven unique, successful, and of tremendous value to future operations. Operations Niagara Falls and Cedar Falls introduced massive jungle clearing in conjunction with tactical infantry operation on a scale never attempted before. A total of 54 bulldozers were under the OPCON (Operation Control) of the 1st Engineer Battalion. . . .

So spoke Lieutenant Colonel Joseph M. Kiernan, Jr., commanding officer of the 1st Engineer Battalion, in summarizing engineer operations during CEDAR FALLS.

Engineer and chemical operations during CEDAR FALLS involved innovative techniques as well as others more familiar and routine. Engineer forces were assigned normal missions such as the construction of a Bigfoot Bailey bridge before the operation to facilitate the movement of the 11th Armored Cavalry Regiment into the Iron Triangle and the clearing and construction of landing zones, roads, and support areas. More unusual projects included the clearing and destruction of enemy underground complexes during search and destroy operations, the stripping of acres of jungle, and the establishment of a waterborne seal at the confluence of the Saigon and Thi Tinh Rivers to prevent enemy escape. The dropping of CS munitions from helicopters and the destruction of rice were entrusted to the chemical personnel.

The engineer-chemical task force for CEDAR FALLS had under Colonel Kiernan's command some six hundred men from the 1st Engineer Battalion, flame-thrower platoons from the 1st Squadron, 4th Cavalry, the "tunnel rats" (tunnel exploration and demolition crews) from the 242d Chemical Detachment, and approximately three hundred engineers from the 79th Engineer Group. This last complement consisted of men and equipment drawn from four engineer battalions, a light equipment company, and a maintenance detachment.

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Bridge on the Thi Tinh

To provide rapid crossing for the 11th Armored Cavalry Regiment and supporting forces as they launched their sweep from Ben Cat toward objectives on the opposite side of the Iron Triangle, the 1st Engineer Battalion of the Big Red One was directed to construct a Bailey bridge over the Thi Tinh River just west of Ben Cat. Work commenced on 21 December, well before D-day, at a site adjacent to an existing Eiffel bridge and a destroyed concrete bridge. The bridge site preparation included the destruction of the remains of the concrete bridge, the construction of headwalls on each bank, and the construction of an eight-pile pier in the center of the river to support the Bigfoot Bailey bridge sections. The assembly of the bridge was begun on 31 December, the launch made on 1 January, and the final welding done by 5 January.

Disaster struck the new bridge on the afternoon of 9 January when a recovery vehicle towing a disabled M-48 tank crashed through the western span. All traffic was halted and an emergency repair crew of the battalion was directed to remove both vehicles from the river and replace the damaged span temporarily with an AVLB (armored vehicle launched bridge). The Eiffel bridge, which had also been damaged by the collapse of the Bailey, was reinforced and opened by 1630, although limited to medium truck traffic. To launch the AVLB, the Bailey span had to be removed from the pier and disassembled- a difficult and time-consuming task. The western approach was extended twenty feet by earth fill and was bolstered by damaged Bailey parts. The shorter (hotfoot) AVLB was successfully launched by 0515 the next morning. The bridge was opened to traffic at daybreak.

Jungle Clearing Operations

During late December 1966 and early January 1967, the engineer task force structure and support role in preparation for the vast amount of jungle clearing for CEDAR FALLS were developed and partially tested in Operation NIAGARA FALLS. The tractor assets from the engineer battalions of the 79th Engineer Group were consolidated under the headquarters of one of its battalions, the 168th, to support the 1st Infantry Division. Experience in NIAGARA FALLS had revealed that the tractors must have an "in-house" maintenance capability to provide on-spot servicing and small repairs; thus, a composite maintenance task force was organized. There also was an attachment from a maintenance battalion which could fabricate parts. Unit and tractor-type integrity was maintained by dividing the personnel and equipment into teams.

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The decision was made to employ the dozer-infantry team. Tankdozers, bulldozers, Rome Plows,* and the infantry would cut into the enemy-infested jungle together, simultaneously clearing the area of vegetation, conducting search and destroy operations, and destroying enemy fortifications.

The dozer-infantry teams used two techniques based upon the tactical situation and the basic characteristics of the equipment. One was a formation of two tankdozers at the point, followed by four bulldozers abreast, with two more dozers as a cleanup team to

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windrow the vegetation that had been cut. Infantry supported the tractors, at the same time carrying out search and destroy missions. The second technique employed a Rome Plow in the lead followed by troops in armored vehicles. When contact with the enemy was made, the men in the vehicles provided fire support until the accompanying infantry could silence the enemy.

A significant advantage of the dozer-infantry team was the additional time it gave the infantry to conduct search and destroy operations. During previous jungle operations the infantry often had been forced to stop to clear resupply landing zones by hand. With the dozers along they could do the clearing, and do it in minutes.

The test of the jungle clearing concepts in NIAGARA FALLS had revealed that the three or four weeks planned for CEDAR FALLS were not adequate to clear the entire jungle in the Iron Triangle. Instead, only 7 or 8 percent of the sixty three square miles of jungle area could be cleared in that time. Therefore, only strategic areas such as those along roads and landing zones would be cleared, plus

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spaced swaths to permit rapid deployment by mechanized and air-mobile units in future operations. The swaths were defined as the operation progressed.

The CEDAR FALLS clearing operations commenced on the afternoon of D plus 1, 9 January, the same day that three engineer base camps were scratched out of the north side of the triangle and spaced along the eight kilometers of road between Ben Cat and Rach Bap. A half mile of clearing along the roadway, fifty meters wide, was also cut that first day. On the following day over 3,300 meters of jungle were torn apart. Also on the second day an engineer platoon with the mission of clearing a landing zone scrambled down the 70-foot ladder from a Chinook hovering over the jungle and joined the 1st Battalion, 28th Infantry, in the Thanh Dien forest. Two hours later the landing zone was ready to receive the first helicopter; later it was enlarged to accommodate four at a time.

In this operation as in most utilizing a large amount of heavy mechanical equipment, the two major problems were fuel resupply and vehicle maintenance. Each dozer team consumed 600 gallons

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of diesel fuel per day. Usually at least six refueling locations- some supplied solely by 500-gallon pods brought in by air-were required daily. Several teams had to be supplied on site by air. When field pumps were in short supply, trenches eight feet deep were dug and the fuel was gravity-fed from the top of the cut into the vehicles. Maintenance problems were compounded by the quantity of equipment involved and the distances between teams. Repairs were made in the field whenever possible; otherwise the disabled vehicle was moved by truck to Lai Khe where heavy maintenance support was provided by elements of the 79th Engineer Group. The maintenance task force operated around the clock and was the significant factor in achieving the very low deadline rate (percentage of vehicles not usable because of needed maintenance) of 10 to 15 percent for tractors and dozers throughout the operation.

Engineer clearing operations continued until 22 January with some impressive results. The jungle area cleared totaled 2,711 acres or 10.9 square kilometers, including 50 to 100 meters of jungle on each side of the major roads in the Iron Triangle as well as 34 landing zones tactically spaced throughout the triangle. Three of the

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zones were cleared by engineers lifted into the jungle by helicopter, the remainder by dozer-infantry teams. In addition, numerous swaths were cut through the jungle, usually in widths from 50 to 100 meters. During the clearing, many small engagements occurred between the engineers and enemy snipers, and, in one instance, an enemy squad. Numerous booby traps were also encountered. However, the 1st Engineer Battalion had only 1 man killed and 7 wounded by hostile action during the operation, while the supporting engineer units had 7 wounded.

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

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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.

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.

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 under-

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ground 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

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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

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

The Engineer Navy

The problem of sealing the confluence of the Saigon and Thi Tinh Rivers in order to prevent the escape of the Viet Cong by water during CEDAR FALLS resulted in another new approach to counterinsurgency warfare, an engineer "navy." The initial plan to deny this escape route to the enemy was to place a force on the banks of each of the rivers. The force would be armed with the newly acquired "quad-.50" machine guns (four heavy machine guns that traverse from a single pedestal and which are fired simultaneously by one gunner). General DePuy believed this mission could be more efficiently accomplished by installing the quad-.50's on platforms placed in the river. The engineers agreed and were given the job.

On 3 January Company E, 1st Engineer Battalion, was directed to procure and load the materials for two rafts to support the weapons and to move the materials to the Vietnamese Engineer School at Phu Cuong, twelve kilometers downstream from the juncture of the Saigon and Thi Tinh Rivers. There each raft was built by connecting two bridge floats with aluminum decking, and a quad-.50 was mounted on each of the platforms. The construction was completed in one day. Additional firepower for each raft was provided by six .30 caliber machine guns, and provision was made for riflemen and grenadiers behind sandbags to be on both the floats and the platform. Eventually dubbed Monitors, each raft was propelled by a 27-foot utility boat.

The navy also included two armed utility boats and several river patrols using pneumatic assault boats. The river patrols consisted of fifteen men: two engineers and thirteen infantrymen. One engineer operated the boat while the other secured it during loading and unloading.

Early on 5 January, with a command helicopter overhead, the engineer flotilla left Phu Cuong and moved up the Saigon River. Approximately two kilometers from its destination, lead elements experienced sniper fire which was immediately countered by machine guns from the rafts and the helicopter; four enemy were killed. By nightfall the rafts were in position at the confluence of the rivers; one raft tied to the east bank and the other anchored in midstream.

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While the Monitors remained in the same general vicinity for most of the operation, the utility and assault boats actively patrolled the rivers. All Vietnamese river traffic was checked and some prisoners taken. In addition the boats ferried supplies to outposts along the river. The navy of the 1st Engineers proved to be a great asset during CEDAR FALLS.

Chemical Operations

During CEDAR Fates the chemical sections of both the 1st Division and 173d Airborne Brigade were used to achieve excellent results in combat operations and in denying materiel and facilities to the enemy.

On 8 January the 1st Division chemical section conducted an experimental drop of 55 gallon drums of CS munitions from a CH-47 (Chinook) helicopter in the Thanh Dien forest in the 3d Brigade's area of operation. On 13 January another drop of thirty drums of CS set to explode at treetop level was made on a linear target approximately fifteen hundred meters long just south of Artillery Base I. Excellent functioning of the explosives and coverage of the target were reported by the Air Force forward air controller observing the drop. On 16 January another 30-drum drop was made on an enemy base camp outside of the CEDAR FALLS operational area. To produce better results on this broad target, two passes were made forming an X with fifteen drums dropped on each pass. Good coverage was again reported. Two more drops were made outside the CEDAR Fates area the next day, again with excellent results. Such drops, when made under controlled conditions in territory in friendly hands, kept the enemy from entering the area of the drop for many days unless he was masked.

The chemical sections were also very active and effective in denying use of captured rice to the enemy. When conditions permitted, the rice was removed from the area. However, in some cases, in view of the large tonnages involved as well as the location of the rice, removal was impossible. For example, on 12 January 450 tons of rice in 100 pound bags, located in eight different caches, were destroyed by the chemical personnel of the 1st Division. To contaminate the rice, a hole was made in the middle of the cache and two 40 pound cratering charges were placed in the hole and detonated. The explosion caused the bags to burst and spread the rice over a wide area. Eight-pound bags of CS crystals were then placed in and around the area, linked with detonating cord, and exploded simultaneously. This system was often and effectively used during the operation.

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Flamethrowers were also employed during Operation CEDAR FALLS for land clearing and against entrenched enemy troops. Flamethrowers provided the best means of destroying the windrows of trees and brush caused by jungle clearing operations. The flamethrower equipped tracked vehicles of the 1st Squadron, 4th Cavalry, were used to burn the green jungle which had been cut. It was found that 2,600 gallons of diesel fuel, 1,500 gallons of gasoline, and 1,500 pounds of chemicals were required to consume four windrows, each 50 meters long. This expensive operation was used rather sparingly. The 2d Brigade also employed flamethrowers to assist in the capture of Viet Cong located in bunkers and tunnels. The flamethrowers reduced the amount of oxygen in the tunnels, to say nothing of producing a significantly adverse psychological effect on the enemy.

The main support of the tunnel search effort by the chemical sections, in addition to the actual tunnel rat teams, consisted of providing different types of air blowers for various uses. One use was to blow smoke into tunnels which had been located (especially those with extremely small diameters which were impractical or

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too difficult to search) to flush out any Viet Cong and to locate other entrances, gun ports, or breathing holes. The Buffalo Turbine, a powerful blower, was often used for this purpose along with 30-pound smoke pots. To assist in locating the smoke exiting the tunnels, observation helicopters as well as troops scouted the area. Because the smoke did not linger, the tunnels could be flushed by the blowers with relative ease so that tunnel rats could almost immediately search the tunnel. On 19 January this kind of smoke operation caused seven Viet Cong to flee a tunnel in the area of operations of the 2d Battalion, 503d Infantry. All were immediately apprehended, suffering from the effects of smoke inhalation. However, after an hour of flushing the tunnel with fresh air, a tunnel rat team was able to search the tunnel with no difficulty. At times the blowers were also used to fill the tunnels with CS.

The Army engineers and chemical teams contributed significantly to the task of destroying the enemy's facilities in the Iron Triangle and making its future use difficult. As Time magazine put it as CEDAR FALLS was drawing to a close, "If the U.S. has its way, even a crow flying across the Triangle will have to carry lunch from now on."

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