FACTS ABOUT TUNNEL RATS

1. In WWII, the Vietnamese resistance dug tunnels to hide from the Japanese. After the war, the Viet Minh continued the tradition and passed it on to the Viet Cong.  By the time the American army arrived, there were 250 kilometers of tunnels in South Vietnam.  Besides hiding places, the tunnels had many of the things you would see at an above ground base camp.  The more elaborate tunnels might have workshops, hospitals, barracks, weapons caches, food supplies.  One tunnel had an American tank buried underground that served as a command center.
2. Once the Americans discovered the importance of the tunnels, they tried several tactics. Of course, bombing came first. That wasn’t effective because the tunnels were too deep and any cave-ins were quickly repaired.  Pumping in poison gas or water was countered with doors similar to those on a submarine.  As a last resort, the tunnel rat program started. 
3. The first tunnel rats were Australian soldiers. It took a special personality to do it.  You had to be brave, intelligent, adaptive, and crazy.  You also needed to be small in stature and less than 5’5”.  The tunnels were usually about 1 yard high and 1 yard wide.  Why would a soldier volunteer for this?  Some saw it as the best way to make an impact on the war.  You find valuable intelligence information or maybe capture a Viet Cong officer.   But most did it for the excitement.  The casualty rate was high and after a while you were flirting with a nervous breakdown.  And many of the survivors ended up with diseases associated with Agent Orange.
4. The Army set up the Tropic Lightning Tunnel Rat school at Cu Chi base camp, which was appropriate because the largest tunnel complex was in the area. The school taught basic survival tactics, but each tunnel rat had his own style.  Most went down with a flashlight and a pistol and a bayonet.  The pistol could be a .45 caliber pistol, but the bang would be so loud that one shot would alarm the whole tunnel.  (Since most went down after throwing in a grenade to clear the entrance area, the enemy knew immediately that something was up.)  Some used a Smith and Wesson .38 with a silencer and an aiming light.  The problem with the aiming light or the flashlight was obviously the enemy knew you were coming and could ambush you.  Since the tunnels were usually not straight, the tunnel rat didn’t know what was on the other side of a bend.
5. Other items carried were probes, a telephone wire spool, remote-controlled explosives, ear plugs (in case you had to shoot, but they limited your hearing), gas mask in case the enemy used gas on you. Smoke grenades to mark tunnel exits for those above ground.
6. The enemy had several counter measures that made the rats’ lives risky. Punji stakes were sharpened bamboo stakes placed under the cave floor with a false floor above.  The stakes might have urine or feces on them to cause infection.  A trip wire might set off a grenade or a swinging spike ball.  Various critters might be encountered as either Mother Nature at her worst or as a type of booby trap.  These included:  bees, rats, spiders, bats, fire ants, scorpions.  And, of course, snakes including one called the “three step snake” because you had three steps before you died.  Or three crawls.
7. There were two operations designed to eliminate tunnel complexes. Operation Crimp in 1966 and Operation Cedar Falls in 1967.  Both were ineffective because the Viet Cong quickly repaired them.  In 1968, the tunnels were used as staging areas for the Tet Offensive.

https://historycollection.com/heartbreaking-truth-behind-iconic-death-scene-elderly-couple-titanic/

https://en.wikipedia.org/wiki/Tunnel_rat

https://www.thenmusa.org/articles/tunnel-rats-of-the-vietnam-war/