User blog comment:MyOpsAreBlackerThenYours/Which time period DLC would you prefer?/@comment-75.182.34.19-20120304004442/@comment-3453223-20120305011524

IIRC They used flamethrowers for clearing out tunnels or throwing grenades in more times than actually walking in. The Vietcong or NVA could stage ambushes and such in there. The first two methods were much more reliable, especially the first. Not only would it catch anyone on fire, but it would suck out all the oxygen in the tunnel, killing anyone deeper inside.