US Army in Vietnam - Operation CRIMP

Operation CRIMP

The air bombardments and the increased use of artillery concentrations had little effect on most of the completed tunnels, and a new problem faced the US infantrymen who would participate in Operation CRIMP: find the enemy's tunnel complexes, clear them, and insure that the enemy could not use them again; until this had been accomplished, no area could be considered safe.

Operation CRIMP was a joint operation - it involved elements of the 1st US Infantry Division, the 173d US Airborne Brigade, and the Royal Australian Regiment and took place in January 1966 in a search of the Ho Bo woods north of Cu Chi for the politico-military headquarters of the Viet Cong's 4th Military Region. Intelligence reports had pinpointed that headquarters as the one which controlled Viet Cong activities in a large part of South Vietnam.

The area in which the operation took place was a rich farming region of Binh Duong province just west of the Iron Triangle. Numerous farms and rice paddies were intersected with hedgerows, rubber plantations, streams, and thick jungle. Since the operation would be conducted during the dry season, the farm land, and even the rice paddies to some extent, provided good cross country mobility for the heavy tracked vehicles that would participate.

Civilians in the area had lived under Viet Cong rule for many years; they had been thoroughly indoctrinated and willingly supported the enemy. Because this was so, one of the early US decisions made was to evacuate the population to a secure location where the people could not interfere with or betray the operation. After an initial interrogation, those civilians not confirmed as Viet Cong members, would be further evacuated to a refugee processing center at Trung Lap.

On 7 January 1966, the 1st Battalion, 28th US Infantry, 1st US Infantry Division, was air lifted from Phuoc Vinh to Phu Loi by US Air Force transport aircraft. From Phu Loi, the battalion conducted an airmobile assault into Landing Zone Jack on the heels of the 1st Battalion, 16th US Infantry; the two battalions had the mission of blocking along Phase Line Pecan until the 2d Battalion, 28th US Infantry could be introduced into an area to the north.

As the 1st Battalion, 28th US Infantry, settled down on the landing zone, the men of the battalion could see that the 1st Battalion, 16th US Infantry was in trouble and receiving fire from the north edge of the landing zone, from the same place that they had to go. The battalion commander, Lieutenant Colonel Robert Haldane, could see that his men were apprehensive, particularly when they saw soldiers from the lead battalion fall under the enemy's fire and grenades.

Because of the firing, Captain Terry Christy, commanding Company B, knew that he had to get his unit off the cleared zone and into the tree line quickly and shouted orders to his platoon leaders and non-commissioned officers to get moving. His orders moved the company into the tree line, but the enemy had suddenly disappeared. Where?

Just a few meters inside the tree line at the edge of a rubber plantation, Christy's men located a large trench, the start of the most elaborate underground fortification complex that the men of the battalion would see for the next several months. But the battalion's mission was to reach a blocking position, and Haldane did not have sufficient time to check out what appeared to be a regimental sized position. Yet it was hard to believe that the enemy soldiers who had engaged the 1st Battalion, 16th US Infantry could have fled undetected through the relatively open rubber trees. Haldane planned to check on this later because his unit would operate in this very same area for several more weeks until the newly arrived 25th US Infantry Division could establish its base camp north of Cu Chi.

As the battalion advanced with three companies on line toward its assigned blocking position overlooking a small stream, reports started filtering into the battalion's command post that cache after cache of rice, salt, and other foodstuff were in the area, enough to feed at least an enemy regiment. That the battalion was, in fact, in a large enemy base complex was further confirmed when the three leading companies reported an extensive mine field across the wooded north end of the area. Apparently, the enemy had planned the area as a permanent complex.

After breaching the mine field, the battalion reached its blocking position where it remained until the 2d Battalion, 28th US Infantry pulled abreast. Then, leaving its blocking position, the 1st Battalion shifted direction and moved to the east, on line with the 2d Battalion.

As the 1st Battalion moved toward Phase Line Pine - the Saigon River - what was once thought to be an enemy regimental camp took on the dimensions of a division base, for during the next two days its soldiers reported foxholes, trenches, mines, caves, and well used trails - but no people - all across the battalion's 1,500 meter front. The march was not completely without incident: soldier after soldier was hit by fire from enemy snipers; Haldane hoped that his men could pin the enemy unit against the river and there take retribution for their losses.

But when the battalion arrived on 9 January at the wide expanse of rice paddies that linked the dry ground with the Saigon River, his soldiers had seen only one or two fleeting enemy soldiers. That night they occupied a deserted village surrounded with foxholes, bunkers, trenches, and mines. Without boats the battalion could not move further to the east.

Then a breakthrough was announced - the 173d US Airborne Brigade and the Royal Australian Regiment to the north had located the Viet Cong, underground!

On the morning of 10 January, the 1st Battalion began retracing its steps, and two hours later one of the companies reported finding a 100-man classroom that had been missed on the previous day's sweep. Fortified with the knowledge of the known successes of the units to the north, Haldane halted his battalion and after establishing all around security, started a detailed search for tunnel entrances.

Finding a tunnel entrance, however, proved not to be easy. A few soldiers reluctantly - lowered themselves into a trench which ran the length of the classroom and then took a sharp bend to the west. Seconds later they reported that the trench led to a hole in the side of a slight rise of ground to the west. Returning to their start point, the soldiers were given flashlights to assist in their further exploration efforts; but they still could not find the sought after tunnel complex. The hole, although extensive, and with steps and a room large enough to contain 100 occupants, was no more than an elaborate air raid shelter. It seemed time to move on to renew the search in another area.

But then it came - the sought after opening! Platoon Sergeant Stewart L. Green, a wiry 130-pound soldier, jumped from the ground with a curse, thinking that something had bitten him. The country was full of aggravating scorpions and snakes so Green had good reason to jump. But as he disturbed the dead leaves on the ground with the muzzle of his rifle, he saw what had "bit" him: a nail! A further search disclosed a wooden trap door perforated with air holes and with beveled sides that kept it from falling through into the tunnel below. The long sought after tunnel had been found, and the shout of discovery brought Colonel Haldane on the run.

The question Haldane had to answer was: what should he do now? The battalion had trained for combat at Fort Riley under an intensified combat training program, but the program had not covered tunnels. Sergeant Green provided the answer to the question as he stepped forward and volunteered to be lowered into the dark depths of the black hole he had so recently uncovered. Like a contagious disease, others standing around the hole volunteered to help Green. Several men followed Sergeant Green down into the hole and within minutes supplies started flowing up from the very bowels of the earth, and bag after bag of supplies were soon on their way to the classroom where Haldane had established his command post.

Captain Marvin Kennedy, the battalion's S2, after inspecting the supplies determined that the unit had uncovered a major hospital Complex. Even as Kennedy looked over the captured booty, a sudden cry turned him around in time to see the soldiers who had entered the small entrance to the underground hospital pop out to the surface as if shot from guns. Sergeant Green was the last out, and he told how he had seen a side passage leading off the main run; as he had looked into the smaller passage, Green said, he first heard and then saw about 30 Viet Cong soldiers in the dim light of a candle that one of them held. He said that the enemy troops had seen him at about the same time and extinguished the candle.

Calling to one of his interpreters, Captain Kennedy asked him to go with Green back into the tunnel to tell the enemy soldiers to surrender. The interpreter agreed and the two men soon disappeared from sight, on a mission that lasted but a few minutes; for when the two men had returned, Green told Kennedy how the interpreter had refused to talk to the enemy troops. The interpreter retorted that he had had to hold his breath in the tunnel because there, was no air and he would have died had he started to talk.

Colonel Haldane decided to seek a different solution and ordered a Mity Mite (a small lightweight, gasoline powered blower) to be brought to the tunnel entrance and turned on. One of the soldiers then dropped several red smoke grenades into the entrance hole while others stuffed their jackets around the air hose of the blower to seal the tunnel entrance as the smoke was pumped down. The soldiers providing security around the area were instructed to look for any sign of the smoke.

For several minutes nothing happened. Then reports came in from every direction of red smoke appearing from numerous holes in the ground. But now a new problem arose: Colonel Haldane had just received orders to destroy the tunnel and to regain contact with the 2d Battalion to the north which was outrunning its flank security, Haldane's unit.

Almost in desperation, CS, a non-lethal, riot control agent, was pumped into the tunnel to rout out the enemy soldiers; but the latter still refused to abandon the tunnel. For a third time Sergeant Green entered a tunnel, this time accompanied by a demolitions specialist. The men placed charges with short fuses in the main tunnel on each side of the secondary tunnel passage, and then made a rapid withdrawal to the surface, warning away all who stood nearby. The earth erupted and an ear-splitting explosion shook the ground; with this accomplished, Haldane moved his unit to catch up with the 2nd Battalion.

But the story was not finished. Two nights later, on 11th January, the battalion returned once more to the rubber plantation on the northern edge of Landing Zone Jack and established a tight defensive perimeter. All of the units participating in the operation - the name of which had been changed from CRIMP to BUCKSKIN - had suffered casualties from random enemy bands who had continued to appear and disappear almost at will. This time, the 1st Battalion occupied the trenches which had been dug by the enemy and which overlooked the landing zone; ambush patrols were put out and the area inspected.

The trench work was quite extensive and ringed the battalion. At the north edge of the perimeter, the trench was fortified with anti-aircraft firing positions; a huge crater caused by a bomb dropped from a B52 bomber raid - 50 feet across and at least 15 feet deep - had hardly damaged the trench or the gun emplacements. In fact, it had collapsed only about a meter of the main trench system.


By now tunnel conscious, the men of the battalion were quick to check out any suspicious looking holes. One of the soldiers pointed out a hole about a foot in diameter which descended into the ground at a 45 degree angle. Some thought it might be an air hole for a tunnel; others thought it might have been caused by a bomb dropped from a B52 which had failed to explode. The hole remained a curiosity until the following day.

It was in the late afternoon when Captain Arnold Larsen radioed that his Company C had discovered an American soldier's helmet at the bottom of a trench and that the helmet covered a booby-trapped mortar round. In a small wooded glade, his soldiers had also found two booby trapped 105mm artillery rounds and a cave with another booby trapped 105mm round in the entrance. Captain Larsen had his soldiers detonate the booby traps by exploding charges placed next to them. He also reported that the first soldier to enter the cave had seen a trap door in the floor, but since darkness was coming on he had decided to place a guard on the door and continue the search in the morning.

The battalion was not to be allowed to rest this night, however, for in the gloom of the rapidly fading light several grenade explosions were heard followed by several quick shots from a carbine. Viet Cong soldiers used carbines and since the shots had come from within the battalion's perimeter, the enemy was inside, too. But how ? And how many were there? Running over to where the action had taken place, in Company B's sector, Colonel Haldane and several members of his staff were met by Sergeant Green and a number of other Company B soldiers, who were standing around a small concrete hatch, shaped like a commode seat on a hinge and perforated with air holes. One of the soldiers said to Haldane: "We were sitting there almost on top of that damn thing heating our C rations, when it sprang open and this Charlie popped up. He threw two grenades, and reached down, grabbed a carbine, and sprayed a few magazine at us before we could even lift our weapons. Then he went back down into the ground."

Sergeant Green once again led a team into an enemy tunnel, and did not surface again for two and a half hours. When he did return, Green reported that he had not been able to find the end of the tunnel; he described it as having an uneven floor which would provide protection should anyone fire down it, and that there were many vestibules in the walls, apparently put there for further protection. Green estimated that he had traveled at least a mile and a half underground before returning. He also requested that he and his men - now called "The Tunnel Rats" - be given several doughnut rolls of communication wire, a telephone, gas grenades, gas masks, flashlights, pistols, and compasses.

When Green was asked whether he wanted to wait until morning before going underground again, he demurred, pointing out that it made no difference in the tunnel as to whether it was day or night on the surface. After a quick meal of rations, Green took his men back into the enemy's tunnel. But this time he could talk with the battalion, and his progress could be measured by the wire as it rolled out. Another group was stationed at the entrance to record Green's progress. Thus, while most of the rest of the men in the battalion slept, Green and his "tunnel rats" were engaged in the hazardous task of exploring the rat-infested tunnel complex.

At the mile and a half mark on the wire, Green called to say that he had spotted a light ahead. His next transmission was more urgent and he notified the anxious men on the surface that he and his group had engaged an unknown number of the enemy in the tunnel. Colonel Haldane told them to don their masks, throw their gas grenades, and return to the surface. This they did, but the firefight continued until Green and his men reached the tunnel's entrance where the soldiers gathered there could hear the dull thuds of the weapons as the men below fired at the enemy. A quick count of the "tunnel rats" caused some concern, for one of the number was reported missing. Green ducked back into the tunnel and found the missing soldier who had crawled past the exit in the dark; as the soldier made his way out of the tunnel, Green held off the Viet Cong soldiers while other members of his team re-entered the tunnel with sufficient explosive charges to block the passageway; the fuse was lit and they scampered to the top.

As the sun came up, Haldane instructed Captain Larsen to raise the trap door in the cave which his soldiers had located the previous evening. When this had been done and the men had climbed through, they saw only a large room, containing nothing more than a basket of grenades; but the soldier who removed the grenades reported that the basket covered a second trap door. This led downward to another large room which contained 148 service records of men who belonged to the D308 Viet Cong Company. Removing the records disclosed still another door, this one leading to a third underground level, and in which a tunnel shaft led away and then branched in two directions. The branch to the west had been rendered almost impassable, and had only a small escape hole just large enough for a small Vietnamese to squeeze through; but the other branch led to the same shaft that Sergeant Green had been in earlier. The hole in the ground discovered in the north portion of the battalion perimeter the previous day turned out to be an air hole for the tunnel.

By this time, the battalion realized that it had entered upon another dimension to the war in Vietnam, and more fully realized it when Company A found yet another tunnel complex the same day. One of its soldiers was killed by a Viet Cong soldier who shot from a small aperture in an ant hill. Several American soldiers rushed the ant hill and discovered an entrance at the rear, while an unattended weapon and a heavy blood trail told a grim story of the effectiveness of their fire. Another pack of "tunnel rats" was born as the soldiers traced the bright red blood through a three-layer tunnel complex that ended 60 feet below the level of the ground, and where a large weapons cache was uncovered as well as the camouflaged parachute from a US Air Force forward air controller who had been shot down in the area on an earlier operation.

But the wounded Viet Cong soldier made good his escape; his trail of blood led to still another opening which was too small for the American soldiers to get through. There was nothing to do but give up the chase.

The experience gained by the 1st US Infantry Division's "tunnel rats" clearly shows that an insurgent or defending force can be expected to burrow underground more and more as heavy bombardment increases. The enemy, therefore, must be cleared from below the ground as well as from the top of the ground before an area can be considered properly secured. Once cleared, the enemy's underground defensive systems must be destroyed, although an enemy can be denied the use of the positions through partial destruction and through the use of the riot control agent, CS. Essentially, though, the underground war can be won in the same manner as the war that goes on above ground: by training in, and the application of, new techniques, and by the use of initiative and sound tactical decisions.

Reproduced from;

Infantry in Vietnam: Small Unit Actions in the Early Days 1965-66
Edited by LTC Albert N. Garland, USA (Ret.), The Battery Press, 1982 Edition





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