The modern day thermal fogger was born from the American colonization of Vietnam in the mid-to-late-20th Century.
Early on in the deployment of US troops to occupy Vietnam, the need for large scale mosquito control became so great that soldiers began improvising insecticide foggers by mounting pesticide sprayers to diesel truck exhaust (Spicknall 1969). The hack turned out to be much more effective, covering nine square miles per day, compared to 50,000 square feet (0.002 square miles) per day using a conventional manually operated fogger (Spicknall 1969).
As the occupation continued, US Army Soldiers were tasked with “rooting out” Viet Cong and People’s Army of Vietnam soldiers, as well as innocents, from tunnels. Tear gas was part of the “Tunnel Rat” (Hemmings 2019) arsenal used to “flush” individuals from caves (Linh personal observations 1966) and was regularly deployed via pyrotechnic grenades and powdered explosives (Rottman 2006).
In 1965, the US Chemical Advisor to the Army’s III Corps (Training Corps) participated in planning a “search and destroy” operation in the Iron Triangle, which was known to house an elaborate Viet Cong tunnel system, and suggested using a Mity Mite fogger to aid in clearing tunnels (US Army 1969). On the first day of the operation (August 8th), the force located a tunnel and set into motion an elaborate scheme to fog the tunnels with hexachloroethane (HC) smoke from burning pots (US Army 1969). Overall, the endeavor was dubbed a success despite the tunnel having been empty already and although only HC was used in this application, it was noted that tear gas would be “very effective in flushing VC from tunnels” should there been any present (US Army 1969).
The practice caught on, as the Army was using foggers to pump “air” or “smoke” into tunnels in combination with “riot control agents” during Operation Cedar falls in 1967 (Lehrer 1968). And by 1968’s Battle of Khe Sanh, it was standard practice to use foggers for tunnel excavation as well as mosquito and fly control (Rottman 2006).