Tunnel Rats

To battle against the Vietnamese and the Cu Chi Tunnels, many United States soldiers were trained to go down into the tunnels, often armed with only a flashlight and a pistol, to scout and look for underground enemy troops.
The following video contains standardized procedure when faced with the prospect of scouting a tunnel, and footage of soldiers going inside:

Ron Giles, a Vietnam War veteran, recounts his experience as a Tunnel Rat in an article with a New Jersey newspaper. He states that he volunteered for the job at first because of his small stature and of thinking that it would be a "one-shot deal". Even though tunneling underground didn't happen frequently, he still had to go down there roughly "two to three times a month". Giles described how if he turned down an assignment he "would have lost respect. [And he] would have lost a lot of face" with his company.
The intense anxieties Giles faced while down in the tunnels can be compared to that of a horror film. Many of his experiences still haunt him to this day; "It's kind of like a catharsis," he said. "But the scariness of it, the horror, the trauma, it just never, never leaves you."

Giles' experience and feelings linked with the tunnels can be compared to that of Tim O'Brien's novel The Things They Carried and how the characters were affected by the war. Many recurring themes within the novel can accurately represent Giles' time at war, such as the fear of blushing and the psychological strain war has on soldiers.

 

http://www.warchapter.com/Vietnam_war_Tunnels.html

http://www.nj.com/news/index.ssf/2009/07/vietnam_veterans_to_share_stor.html