Between World War I and the Vietnam War. Flamethrowers were deemed inhumane due to the devastating effects both psychologically and physically caused by the sticky fiery liquid. While there is no explicit international ban on flamethrowers, they were officially retired from the US military arsenal in 1978 by the Department of Defense. (Pic: flamethrower tank from 3rd Marine Division in action near Da Nang, Vietnam, dated January 1966. Wikimedia Commons photo.