Over 20 years ago, I had an employee who was a former tunnel rat (Marine or Army, I don't remember). He was not much for talking about his experiences, but told me once he used a .38 revolver. What kind, I don't know. He bought a ticket home by running over the edge of a cliff while fleeing a VC ambush and breaking his back. He was about what you'd expect as a tunnel rat, a small, wiry guy. The experience definitely had a lasting effect on his (unusual) personality.