In Vietnam, almost all tunnels were initially hit with the M7A2 series of CS. There, however, was another way that they placed CS in the Tunnels. That was by pumping it into an opening of the tunnel. The name of some of the machines used were the: "Military Disperser, Portable, Riot Control, Agent, M3", "Military Desperser, Riot Control Agent, Helicopter or Vehicle Mounted, M5", GOEC MK And MK-XII-A Pepper Fog, or even the "GOEC MK-17 Pepper Fog.
CS grenades including the XM58 were used by SOG across the borders. Ocassionally, in Combodia and even lesser amounts to be used in Laos were the air droppable CS weapons from "Fast Movers". Whenever the request was made to use them for a RT in bad in deep doodoo, the FAC had to request it to CINCPAC then to the Ambassador of either country in which was to be used in. This usually took no more than an hour to get a reply. So they would go ahead and use it anyways and just move the men in closer to the Vietnam border on paper because those maps were far from perfect back then If you know what I mean.
Allot of RT's and their members were saved by doing this, and it WORKED!