Special US Soldiers called ‘Tunnel Rats’ Would Crawl through the Systems to Find the Enemy
The Vietcong used elaborate tunnel systems to store food and ammunition as well as housing medical and combat facilities. The largest tunnel systems in South Vietnam (some under US bases) could be as vast as 200 kilometers (125 miles) long and were built to withstand bombings, explosions, poison gas etc. Many of the systems were built using forced labor from surrounding villages.
My Vietnam Experience 