Appendix

APPENDIX B

As described elsewhere in this book, the effective tactical deployment of tunnel warfare evolved over many years, but there is no evidence to suggest that there was ever a ‘master plan’ to build the networks of tunnels in the form that they eventually took.

However, it’s clear from the following document—discovered by Korean forces in September 1967 and translated into English long after 3 Field Troop had been and gone—that having realised the strategic value of their tunnels, the North Vietnamese weren’t keen to leave anything to chance.

This document is basically a ‘how to’ training booklet on tunnel planning, building and operations, outlining the preferred design of tunnels and discussing their uses, construction, specifications and maintenance.

It details everything from the size of the entrances and their positions relative to each other to the numbers in digging teams and what they should do with the soil they pull out of the ground. It also reveals how important the tunnel systems were to the Vietcong, referring frequently to the reason for their existence being simply that they were out-gunned by the Allies.

The document gives us a remarkable insight into the thinking behind the tunnels. These days, knowing the commitment, ingenuity and industry of Vietnamese people, it’s little wonder that they had made a science out of their construction, location and operation.

Construction of Underground Tunnels in Combat Villages and Hamlets

FOREWORD

Underground tunnels have existed for a long time, and their construction requires special building techniques. No documents on this subject, however, have ever been issued. Recently, the task of digging underground tunnels depended mainly upon the ability of the people in local areas. As a result, the methods adopted were different and the effectiveness of underground tunnels was highly variable.

In some local areas, the underground tunnel met the required conditions as expected; in other areas, however, their role was misunderstood. Because of the people’s lack of basic technical knowledge, the tunnels were either unusable after much manpower had been expended or became mere shelters instead of strong combat posts.

This document compiles the basic technique of construction with the experience gained in local areas. Its purpose is to provide technical assistance for combat villages and hamlets. I will exclude all tactical matters. Though the document refers to the experiences gained in many different places, it is still far from adequate. We expect to see it enriched with more suggestions and ideas from the local areas and from various units.

I. The role and effectiveness of Engineer Section underground tunnels in combat villages and hamlets

1. The role of underground tunnels:

The war has become increasingly fierce. The enemy is trying to paralyse our combat potential with intensive air and artillery attacks. In the face of this situation, we should realise the necessity of the people’s warfare. We must overcome all difficulties in order to intensify guerrilla activities in support of a war of movement.

The primary role of underground tunnels is the strengthening of combat vitality for our villages. They also provide more safety for our political and armed units, and for the masses as well. But their sheltering purpose is only significant when they serve our soldiers in combat activities. As mere shelters, their great advantages are wasted. Their construction should therefore be in accordance with the combat plan as drafted by the villages and hamlets. There should be combat posts and equipment inside the underground tunnels for providing continuous support to our troops even if the enemy occupies the village. The armed forces must be able to enter one passage of the underground tunnels and exit from another or disappear and appear suddenly in order to attack the enemy.

Furthermore, we should plan for the eventual impossibility of fighting from inside the underground tunnels. A secret passage must then be available from which our troops may escape and fight in the open, or re-enter the underground tunnels, if necessary.

2. The effectiveness of underground tunnels :

a) They strengthen the combat vitality of villages and hamlets: If the underground tunnels are dug so as to exploit their effectiveness fully, the villages and hamlets will become extremely strong fortresses. The enemy may be several times superior to us in strength and modern weapons, but he will not chase us from the battlefield, because we will launch surprise attacks from within the underground tunnels. We can see then that underground tunnels are very favourable for armed forces as limited as are ours in strength and weaponry.

b) They reduce the advantage the enemy has, of superior firepower: Effective underground tunnels help our forces launch close-in attacks on the enemy, while providing opportunities for the seizure of weapons.

c) They enable our forces to wear down the enemy’s potential with relatively few weapons.

d) They provide more mobility for our troops: We may attack the enemy right in the centre of his formations or keep on fighting from different places.

II. Influence of the terrain upon underground tunnels

The terrain in different areas may influence the underground tunnels differently according to the undercurrents, nature of the soil in this document: Midland and mountain areas; Lowland and populated areas

1. Midland and mountain areas:

Digging underground tunnels in midland and mountain areas often takes much time, manpower and materials, because there are a great deal of rocks, and tree roots. But the tunnels in these areas are strong. We need few supporting poles, and water is more easily drained.

2. Lowland and populated areas:

The soil in these areas is usually soft and saturated with water. In the rainy season, the earth can slide. There must be many poles set up to support the tunnels, so the cost of materials is correspondingly higher. In sandy areas, there must be frames for supporting the roof and walls of the underground tunnel, and covers for the openings (in lowland and coastal areas). The most difficult problem is that of draining water and strengthening the tunnels against landslides. This should be given particular notice, if we wish to render the underground tunnels most effective.

III. Basic principles of the construction of underground tunnels:

The construction of underground tunnels must be based on the following principles: the terrain where the underground tunnel is dug; the enemy situation; the friendly situation.

1. Terrain:

The terrain directly affects our combat activities and tactics as well as the cost of manpower and materials. There must be a careful selection of the terrain before the construction of underground tunnels is begun. This is an important precaution to consider in our preparatory work.

2. The enemy situation:

The main purpose of the underground tunnel is to increase our combat capability. The enemy has always tried to destroy our underground tunnels. Some local areas, however, made very little use of their underground tunnels, though they had invested a great deal of manpower and materials to their construction. They ignored the enemy situation and failed to coordinate the effectiveness of underground tunnels with combat plans when the enemy attacked. They should have studied the enemy’s operating methods and possibilities of attack before beginning the construction of underground tunnels. NB: Lessons should be drawn from the enemy’s previous sweep operations.

3. The friendly situation:

The digging of underground tunnels must be carried out in accordance with the organisation and equipment of the village and hamlet militia and guerrilla units. All the possibilities of manoeuvring manpower and providing materials and tools must be considered and planned beforehand.

IV. Principles, technical requirements and distribution of work

A. Principles

In order to maintain security and prevent the enemy from discovering and destroying our underground tunnels, the following principles must be observed:

• Select an appropriate location for the underground tunnel.

• Determine the location of the entrance into the underground tunnel.

• Determine the location of the angles and passages in the underground tunnel.

1. How to select the location:

a) The underground tunnel must be located where it serves combat activities most effectively. It is constructed more for combat than for shelter purposes. If it fails to meet the actual requirements of the situation, it will create difficulties for our soldiers.

b) Select dry areas or places where the water table is very deep underground. Elevated areas are most preferable, because flooded, damp areas will require much manpower, time and materials and the underground tunnel will be subject to slides and cave-ins.

c) Select easily camouflaged areas: secrecy is an important factor in rendering the underground tunnel strong and effective. Secrecy also provides opportunities for launching surprise attacks.

Well-camouflaged areas protect our soldiers from detection by the enemy. NB: Camouflage should by no means disturb the movement of our troops in combat.

2. Entrance into the underground tunnel:

a) Pre-construction tasks: The soil selected for underground tunnels in lowlands should preferably be mixed with gravel and rocks, because it will save on manpower and time. Furthermore, the cadre in charge of selecting the location should examine the terrain carefully.

b) Secrecy and surprise: Surprise is an extremely important factor in the war against the enemy. We continually try to destroy the enemy, and he does likewise to us. While selecting the location, the cadre must take into consideration both future combat activities and the surprise factor that enables us to attack the enemy without being detected by him.

c) Possibilities for raids: Because the activities of the militia and guerrillas require appearing and disappearing quickly, the entrances to the underground tunnel must be located like the corners of a triangle, so that each can support the other in combat. Our troops must be also able to escape from the underground tunnel, through a secret opening, so they may continue to fight.

d) Measures against floods and asphyxia: As we know, the US Imperialists make use of highly lethal weapons in order to kill us and attain their vicious end. They drop explosives and incendiary bombs, and even pour chemicals into our underground tunnels. For this reason, we must locate the entrances to the tunnels in dry, elevated and well-ventilated areas. Such an entrance will not be blocked by the chemicals that will otherwise kill the occupants. Also, rain water will not stagnate in an entrance so located.

3. Corners and passages in the underground tunnels:

a) Corners: The passages in the underground tunnels must not all be straight or snake-like. They must be made in 60° and 120° angles; that is, not less than 60° but not more than 120°.

b) The passages: They must be neither too broad nor too narrow. The nature of the soil as well as the strength of troops using them must be studied before they are dug. Underground passages should not be dug underneath common paths, because the enemy will discover them easily.

4. Thickness of the roof:

The minimum thickness of the roof must be 1.5 metres, if we wish to avoid vibration caused by the explosions of bombs and shells, and the sounds of mechanised units moving above.

B. Technical requirements and distribution of work

1. The different parts and the technical requirements:

a) Entrance: It must be hidden and easily camouflaged; it must serve combat activities; it must be favourable for our fields of fire; it must have accurate dimensions.

• It must be hidden and easily camouflaged: The construction of underground tunnel entrances has been misunderstood recently in some local areas. They dug the entrances in open areas, possibly to help the diggers remove the earth more rapidly. They did not realise the importance of secrecy. Their carelessness enabled the enemy to discover the underground tunnel easily. We should therefore dig hidden, easily camouflaged entrances to ensure safety for our soldiers and weapons.

• It must serve combat activities: Though the technical side of digging entrances is important, the tactical side should not be disregarded. We noted that most underground tunnel entrances in local areas were not located as they could support each other. They were dug in straight lines. The cause for the error was that they were regarded more as a place for exit and entrance than as a fortification for success in combat. The entrances must be located in triangular form. The distance between two entrances depends upon the firing range of their defenders. The average distance is 40 to 50 metres.

• Distance between the entrances: In some local areas, the entrances were located only a small distance from each other. They were only 10 to 12 metres apart. Worse still, in some places, they were just 5 to 7 metres apart. The reason was that the digging was entrusted to separate families or groups of persons, who could not foresee the disastrous effects of their thoughtlessness. Though a number of entrances were later filled up, we noted that this deficiency has been carried over in many other local areas. They seem to ignore the fact that close entrances attract the enemy’s attention and do nothing but assist his discovery.

As far as actual experience has taught us, the distance between two entrances should be at least 20 to 30 metres. Difficulties will certainly arise, because at such a great distance, the diggers may deviate from the planned direction and their output may be reduced. But we gain the advantage of maintaining the secrecy of our underground tunnels.

• Accurate dimensions: The entrance of an underground tunnel must be strong. We need to expend a great deal of manpower, time and materials to make it so. The following dimensions are to be adopted:

—Square entrance 1.5 metres for each side

—Rectangular entrances 1 metre × 1.8 metres

—Round entrances 1.5 metres in diameter.

Recently, local areas have observed no systematic digging procedure. Some entrances were too large and remained weak; thus time, manpower and materials had been wasted. The local people tried to correct the blunder, but their hasty work caused additional earth to cave in and help the enemy discover the entrance. Small entrances are stronger but they disturb our movement and render entering or exiting difficult. In short, both large and small entrances are ineffective. We therefore recommend the above dimensions, which we hope will be studied and utilised by all local areas.

b) The passages: The following requirements must be met if we wish to allow safe and successful fighting from the underground passages:

—The passages must not be wider than 1.2 metres

—They must not be narrower than 0.8 m

—They must not be higher than 1.8 m

—They must not be lower than 0.8 m

—Their angles must not be smaller than 60°

—Their angles must not be larger than 120°

—Their directions must be accurate

—They must have by-passages and several floors.

• Why must they be neither wide and high, nor narrow and low? Digging wide, high passages requires much time and manpower. Such passages are usually weak; they shake or cave in when disturbed by bomb and shell explosions. Low, narrow passages, on the other hand, save time and manpower, but they disturb the movement of troops and affect our combat activities. We can therefore conclude that the size of the passage depends on the nature of the soil, the number of troops occupying the underground tunnel and the possibilities of troop movement. The above dimensions are expected to be the most favourable.

• Why must they be dug in a zigzag fashion? Most local areas have recently made the passages of their underground tunnels snake-like, or even in straight lines. This is dangerous, because if the enemy detects the entrance to the underground tunnel, he will set off mines and bangalores [extended tube bombs] or pour in chemicals, both of which are certain to have disastrous effects on our troops. This is why we must dig the passages in a zigzag fashion and provide covers at the corners and between the floors.

• Why are by-passages and floors necessary? Probably because they were entrusted task work and wanted to build their underground tunnel more quickly, or because of a lack of guidance from cadre, most of the local areas built their underground tunnels with one floor and few or no by-passages. The enemy will detect these underground tunnels easily and we will meet difficulties because of these deficiencies.

In order to permit safe and continuous fighting by our troops, they must be able to hide in another by-passage if one is discovered or escape to another floor if one is destroyed by the enemy. This explains the necessity for building an underground tunnel with several by-passages and floors. At the entrance to by-passages and separate floors, there must be covers and other materials for fire prevention.

c) Correct direction: There are two ways to maintain the right direction when we dig underground tunnels: with devices; with the manual procedure.

• We introduce here the manual procedure: After examining the terrain, studying the combat plan carefully and determining the dimensions, we begin to dig in many spots at the same time. It is difficult to make the two ends connect, of course, because our technical skill is poor and we lack facilities. To overcome this difficulty, we must dig many openings 20 to 30 metres apart and regulate the direction by producing sounds. NB: Nearby openings help us adjust the direction more easily, but they facilitate enemy detection, even if they are later filled up and camouflaged.

2. Working methods:

a) Design and marks: At first, the cadre must study the location carefully. Then, they plant banners, poles or reference sticks to mark the different areas as required by the combat plan: the entrance, the passages, the direction, the corners and so on. After that the digging may be started.

b) Disposition of manpower: From the moment they receive the mission, they must study the location, and examine the situation until they assign tasks and responsibilities to individuals. The cadre must spend on this a considerable amount of time. We offer some suggestions as to an effective distribution of work, and hope that the local areas will gain more experience in the process of building their underground tunnels.

—two persons will dig and shovel earth from the tunnel

—one person will rake the earth out of the opening.

These three persons will rotate their work.

We do not mention the number of persons needed for removing the earth will be removed and thus depend on the specific local areas [sic]. ‘Swing-excavators’ [a bamboo crane-excavator] are desirable to remove the earth more quickly from the tunnels, because the roof of the tunnel must be 1.5 metres thick, so we must dig down into the ground to a depth of 2.5 to 3 metres.

In case the entrance of the underground tunnel cannot be located behind concealment, the diggers must fill superfluous openings according to the requirements of the combat plan. NB: There are two ways of placing the wooden supports or bamboo poles (10 centimetres in diameter) in the openings: place them horizontally; place them vertically. The wooden supports or bamboo poles are placed horizontally and close together in the opening. They are covered with bamboo wattles, then with a thick layer of clay, to prevent rainwater from entering. Over the layer of clay, another layer of well-pressed earth is added to make the openings level with the surface of the ground. Of course, the horizontal wooden struts or bamboo poles must have supports under them. The vertical struts or bamboo poles must also be placed close to each other. They are covered with well-pressed earth.

This method is only adopted when we must fill in the openings at the extreme ends [sic]. The layers of earth must be strongly pressed to prevent the enemy from discovering the many openings (in which case, he sets off mines and bangalores or pours smoke into the underground tunnels). The entrance to an underground tunnel is preferably located in bushy, concealed and unexpected places.

Not far from the entrance, there must be combat fortifications (or combat posts). Our soldiers will be able to fight from these posts before they enter the underground tunnel or after they leave it. The fortifications must not be too close to the entrance because they will betray its presence. Covert ways connecting them with the passages of the underground tunnel are also necessary.

c) The passages: The passages are dug in the following ways: with digging devices; with the hands. We introduce here the way to dig passages with the hands.

• Manual digging: The passages are usually dug by: two persons who rotate in digging and in shovelling the earth; two to three persons who remove the earth (depending on how far the earth must be removed). The total is four to five persons.

• Notice: The earth removed from the underground tunnel should be made into basements for houses, furrows for potato growing or banks for communications and combat trenches. It may also be poured into streams but must never be left heaped in mounds. In short, the utmost care must be taken to conceal the underground tunnel from the enemy’s discovery.

d) Equipment in the underground tunnel: As we know, the enemy is very dangerous. He drops hundreds of tons of bombs and fires thousands of shells on our villages to kill cattle and innocent victims. He also destroys the people’s crops with chemicals. In sweep operations, the enemy soldiers try to destroy our underground tunnels by setting off mines and bangalores, or by pouring in chemicals, smoke or water. If we want to fight him both in the open and in underground tunnels, we need to equip them adequately. The underground tunnels are protected on the outside by combat posts, spike pits, mines and booby traps. They must also be well equipped inside for combat.

• Combat equipment: In emergencies, our troops enter underground tunnels. They must be able to continue fighting. To help them do so, we must build our underground tunnels with several by-passages, floors, openings and covers. At the corners and between the floors, there must be strong covers to protect us from mine and grenade fragments. We must also dig spike pits in underground tunnels which we cover normally for safety. We may also lay mines and grenade traps in advance but should not fix the wires. When the enemy enters the underground tunnel, we must be able to sneak into a by-passage or to another floor before the mines and grenades are set in the armed position. The covers will serve to protect our troops from smoke and chemicals. The following two ways are adopted for making covers:

With boards 1 centimetre thick and 2 to 3 centimetres wide, make two frames: one with horizontal boards and the other with vertical boards. Insert a nylon sheet between the two frames which later will be glued together. Cover it with sponge rubber and fill all openings with wax. NB: A single board should never be used for a frame, because it is not strong enough.

Another type of cover can be made in the form of a bottle cork. One man can sneak through the opening and shut the cover after him. NB: The cork must be covered with a plastic sheet.

• Equipment for activity: The underground tunnel must be well equipped inside, just as it is outside. There must be resting places, areas for wounded soldiers, food storage points, latrines and urinals, and ventilation shafts. (There must be several ventilation shafts turned towards the wind.) To prevent the underground tunnel from being flooded, a hollow must be dug every 20 to 30 metres. It should be 20 centimetres wide, 15 centimetres deep and serves to contain drain water.

Furthermore, we must prevent detection by the enemy’s dogs and not allow snakes to enter the tunnels. For this purpose, we must scatter some garlic or powdered pepper at the entrance or near the ventilation shafts. NB: Avoid staying in groups. The dogs will detect our presence and the enemy will discover the underground tunnel more easily if we are in groups.

V. Camouflage

Camouflage is very important, because it reduces the number of the enemy’s opportunities to discover our underground tunnel. We must think of camouflage continuously once the underground tunnel is built. It should be done so skilfully as to blend the entrance of the underground tunnel with the terrain and natural environment. Manioc or sweet potatoes may be grown on the entrance, as experience has proven. But the best way to maintain secrecy for the underground tunnel is, as ever, to indoctrinate the local people with a firm determination to turn deaf and dumb to the enemy’s enquiries.

VI. Supervision and maintenance

Supervision and maintenance have recently been neglected in many local areas. Damaged areas were not discovered in time and repaired. We should therefore have specific plans for supervision and maintenance, and repair damage in case cave-ins or fissures occur (by making support frames).