Chu Chi is just outside the suburbs of Ho Chi Minh City which was Saigon back during the Vietnam War.  I remember when I was in my late teens how South Vietnamese or American forces numbering thousands of men would conduct search and destroy missions against large formations of Viet Cong (Communist Vietnamese) soldiers, ostensibly surrounding and trapping the enemy, only to have it evaporate into the jungle in one Houdini disappearing act after the other.   The mystery behind those disappearing acts is now obvious.  Starting in the late 1940's and ending in the 1960's the Vietnamese built thousands of miles of tunnels throughout Vietnam with hundreds of them being dug close to and sometimes underneath American and South Vietnamese lines close to Saigon.  Inside the tunnels the Vietnamese enemy--they were called the Viet Minh while fighting the French and later the V. C. when pitted against U.S. soldiers erected hospitals, munitions warehouses, and fighting centers that defied  all attempts to locate or destroy them. 

Such tunnel systems usually consisted of at least three levels.  Although the first level could be knocked out by direct hits from American bombs the third level was nearly immune.  And should gas be directed into the tunnels cleverly designed water traps dissipated such gases quickly and long before they could get into the farther or deeper recesses of the labyrinth.  This left the job to individual American soldiers who had to venture into the closed confined claustrophobic spaces that the Vietnamese were intimately familiar with.  After all, they lived down in the tunnels for years where they left a large variety of booby traps for the intruders to discover from poisonous snakes to grenades along with numerous types of impalement devises designed to drive a single spike into a man's foot or an entire array into his entire body.

It took a special kind of soldier who had the physique and requisite guts to go after the Vietnamese hiding in the tunnels.  Even so, undoubtedly, more tunnel rats must have been killed than they killed in return.   To discover just what it took to ferret out the enemy in the tunnels click here.