https://medium.com/@willrussell_46069/life-of-a-tunnel-rat-in-vietnam-ab1fe5394232
Background to the Tunnels
During the First Indochina war against French colonial forces, the Viet Minh constructed an extensive system of underground tunnels, which were later expanded by the Viet Cong.
There were two types of tunnel —
Expedient tunnels — Simple in construction. Size ranged from twenty to several hundred feet long. Consisting of ambush, safe hide, river bank or escape tunnels. Carefully camouflaged entrances to facilitate evasion and escape.
Complex tunnels — Tunnel may be a misleading word. They were more underground complexes which housed hospitals, sleeping quarters, training areas and arms depots. Sophisticated ventilation systems allowed soldiers to stay underground for sustained periods of time.
Cu Chi Tunnel Complex
An example is the massive tunnel complex in the district of Cu Chi, just 20 miles north of Saigon. Cu Chi was one of the most bombed and devastated areas in the war, indeed in any war. Yet the tunnels persevered. They housed thousands of troops.
The access holes were breathtakingly small — some measuring 2 feet wide by 3 feet deep — led to tunnels connected by hidden trap doors that zigzagged up, sideways and down. These tunnels led to a labyrinth of caverns and caves. That spread across up to four levels for two hundred miles, stretching all the way to the Cambodian border.
There was air and sanitation — but they were very basic. You could exist but it was just existing. The mazes were usually less than six feet high. You lived there. You slept there. The occupants took all they required into them. They lived like that for years. Weapons were built down there at primitive forges. They hid the bodies of their troops in them to make their casualty count lower to the enemy. Babies were born in the tunnels. Doctors worked on the wounded using the most basic surgical tools and honey as antiseptic. Anesthetics were rare.