Abstract
At the peak of the Vietnam War, the network of tunnels in the Iron Triangle and Cu Chi linked Viet Cong (VC) support bases over a distance of some 250 km, from the Ho Chi Minh Trail and Cambodian border to the outskirts Saigon. In the early 1960s, the United States escalated its military presence in Vietnam in support of a non-Communist regime in South Vietnam. The North Vietnamese and VC troops gradually expanded the tunnels. Tunnels frequently were dug by hand in Old Alluvium terraces, and only a short distance at a time. Four major efforts were made by the US Military to locate and destroy these tunnels. These included Operation Crimp, a search and destroy mission which began in 1966 and a geological and soil survey approach was used to detect VC tunnels. Later in 1967, General William Westmoreland tried launching a larger assault on Cu Chi and the Iron Triangle areas. The operation called Operation Cedar Falls was an expanded version of Operation Crimp. Finally in 1969, B-52s started carpet bombing the Cu Chi and Iron Triangle areas and destroyed many of the tunnels. However, not before the tunnels had proven very effective in 1960s at hiding and protecting the VC during US occupation of the area. The nature and properties of the Old Alluvium soils were key to the soil tunnels being so resilient. Soils located in Old Alluvium terraces had high levels of clay and iron. Iron (Fe) leached from the upper soil layers (0 to 1.5 m) and accumulated in the lower layers (1.5 to 20 m) and became a cement-like binding agent. When dried the soil layers took on properties close to concrete, and were resistant to ever becoming soft and moist again especially around the aerated tunnel walls. The tunnels were dug in the monsoon season when the upper layers of soil were soft and moist but not in dry season. The soils were highly stable without any lining or support. After drying out, the soil materials surrounding the tunnel turned into concrete like material that could withstand adjacent explosive blasts.
Highlights
The soils of Vietnam (Figure 1) formed from the humid topical climate and diverse geography of Southeast Asia have shaped Vietnam’s ethno-cultural relations, its turbulent history and economy, and its borders as it became a nation
In this paper we examine the unique properties of Old Alluvium soils and conditions that made them well suited for the tunnels built near Cu Chi and the Iron Triangle north of Ho Chi Minh City along the Saigon River in southern Vietnam (Figure 2) and the role these tunnels played in protecting the North Vietnam forces when they invaded Saigon and South Vietnam in 1968
The Cu Chi and Iron Triangle tunnel systems are northwest of Ho Chi Minh City (Saigon) (Figure 2) and both tunnel systems were used by Viet Cong to get from Ho Chi Minh Trail at the Vietnam-Cambodian border to Saigon and South Vietnam
Summary
The soils of Vietnam (Figure 1) formed from the humid topical climate and diverse geography of Southeast Asia have shaped Vietnam’s ethno-cultural relations, its turbulent history and economy, and its borders as it became a nation. Less well known is how its Old Alluvium soils provided the raw material for tunnel building used for housing and guerilla warfare against colonial occupiers for centuries. The primary objective of this paper is to determine how the Cu Chi and Iron Triangle tunnels systems survived over two years of US bombing and still allow the Viet Cong to invade South Vietnam during the 1968 Tet offensive. In this paper we examine the unique properties of Old Alluvium soils and conditions that made them well suited for the tunnels built near Cu Chi and the Iron Triangle north of Ho Chi Minh City (formerly Saigon) along the Saigon River in southern Vietnam (Figure 2) and the role these tunnels played in protecting the North Vietnam forces when they invaded Saigon and South Vietnam in 1968
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