A cross section from the tunnel system

This area was also the termination of the Ho Chi Minh Trail. Because of this, the Củ Chi and the nearby Ben Cat districts had immense strategic value for the NLF (National Front for the Liberation of South Vietnam). Mai Chi Tho, a political commissar stationed in Củ Chi describes the region as a “springboard for attacking Saigon.” He goes on to say: “We used the area for infiltrating Saigon-intelligence agents, part cadres, sabotage teams. The Tết Offensive of 1968 was preparedthe necessary troops and supplies assembled in the Củ Chi tunnels.”
In the beginning, there was never a direct order to build the tunnels; instead, they developed in response to a number of different circumstances, most importantly the military tactics of the French and U.S. The tunnels began in 1948 so that the Viet Minh could hide from French air and ground sweeps. Each hamlet built their own underground communications route through the hard clay, and over the years, the separate tunnels were slowly and meticulously connected and fortified. By 1965, there were over 200 kilometers of connected tunnel. As the tunnel system grew, so did its complexity. Sleeping chambers, kitchens and wells were built to house and feed the growing number of residents and rudimentary hospitals created to treat the wounded. Most of the supplies used to build and maintain the tunnels were stolen or scavenged from U.S. bases or troops.
The medical system serves as a good example of Vietnamese ingenuity in overcoming a lack of basic resources. Stolen motorcycle engines created light and electricity and scrap metal from downed aircraft were fashioned into surgical tools. Doctors devised new methods to perform sophisticated surgery. Faced with large numbers of casualties and a considerable lack of available blood, Dr. Vo Hoang Le Ly came up with a resourceful solution. "We managed to do blood transfusion," Vo said, "by returning his own blood to the patient. If a comrade had a belly wound and was bleeding, but his intestines were not punctured, we collected his blood, filtered it, put it in a bottle and returned it to his veins.”
By the early 1960’s, the NLF had created a relatively self-sufficient community that was able to house hundreds of people and for the most part, go undetected by American troops based, literally on top of the tunnels.