What were these tunnels and how did tunnel rat soldiers come about?
During the Second World War, the Vietnamese first constructed underground tunnels to fight Japanese invasion. In the 1940s and 1950s, the Vietnamese expanded these tunnels to hide nationalist guerrillas known as the Viet Ming. These guerrillas were fighting the colonial power of France. Major Nguyen Quot, an officer that spent ten years in these tunnels, notes that by 1948 they “already dug a tunnel system: each family, each hamlet, had a tunnel communicating it with others”. By the time the American army arrived, there were over two hundred kilometers.
Initially, America used hunting dogs to locate the enemy. Once the Viet Cong caught on to what was happening, they began to use the same soap the Americans used. This way, they smelled the same as the GIs and the dogs became unable to locate the enemy. The US army now sought alternate measures. Americans often carpet bombed areas under suspicion to try flushing out the enemy. The bombs caused earthquakes that destroyed the tunnels and their ventilation shafts. If it did not force the enemy out, those inside the tunnels often suffocated to death instead.
In a more direct attempt to seek out the enemy, US soldiers used portable turbines to blow CS gas into tunnel shafts they located. Again, those inside suffocated. Another method frequently used attempted to flood the area so badly that the enemy desperately sought to escape to avoid drowning. Using this tactic, they added yellow dye to the water to enable aerial observers to spot any entrances that ground troops had missed.
Yet, both of these tactics were not as successful as they hoped. What they failed to realize is that many of the tunnels had several layers and doors built into them to help prevent such fatalities. The Viet Cong built drain pipe ventilation shafts every 20 to 30 meters at an oblique angle to prevent flooding. Tunnels were also built in zig-zags to prevent the enemy from pouring in chemicals or shooting bullets over a long distance.
On average, tunnels in this underground network were 1.2 meters wide and only 0.8 to 1.8 metres high. As a result, sending a soldier underground, known as a tunnel rat, was often a final measure if all other methods had failed.