Flamethrowers are widely considered one of warfare's most controversial weapons and are capable of inflicting gruesome physical injuries and intense psychological trauma.Despite being the last of the major combatants in World War Ⅱ (WWⅡ) to develop them,the U.S.military quickly became the most frequent and adept operator of portable flamethrowers.This gave the U.S.military ample opportunity to observe the effects of flamethrowers on enemy soldiers.However,while most people in modern times would consider immolation by flamethrower to be an unnecessarily painful and inhumane way to inflict casualties,immolation was,at one point during WWⅡ,referred to as “mercy killing” by the U.S.Chemical Warfare Service (CWS).This mischaracterization arose from a series of first-hand accounts describing what were believed to be quick,painless,and unmarred deaths,as well as from a poor and incomplete understanding of flamethrower lethality.As a result,indirect mechanisms such as hypoxia and carbon monoxide poisoning were generally absent from accounts of the flamethrower's fatal effects.It was not until several years after flamethrowers were introduced to the frontlines that the CWS and National Defense Research Committee (NDRC) conducted a series of tests to better understand the physiological and toxicological effects of flamethrowers.This article examines how the initial absence of scientific data on the physiologic effects of flamethrowers led to an inaccurate understanding of their lethality,and bizarre claims that one of history's most horrific instruments of war was considered one of the more “humane” weapons on the battlefield.