Sgt. Fernando Herrera (center), Sgt “Killer” Kaiser (right), and two fellow soldiers take a moment to relax at night in Vietnam. “Tunnel rats” like Kaiser were slightly-built soldiers who crawled through North Vietnamese tunnels fighting North Vietnamese soldiers and Vietcong. After the Vietnam Conflict ended, it was discovered that Cu Chi had the highest number of tunnels in Vietnam, and the site included a hospital. Cu Chi, Vietnam, circa 1968.