As a weapon, fire was limited in its effectiveness by the difficulty of controlling and delivering it. The Chinese are credited with the first controlled wartime use of fire about 500 b.c. Other ancient peoples used pots full of burning oil to defend city walls against invaders attempting to scale them. Around 671 a.d., the Byzantines successfully defended Constantinople by using Greek fire against the Arabs. For centuries, the ingredients of Greek fire were kept a closely guarded secret, but eventually the Arabs were able to acquire it. The Middle Ages also saw the use of fire arrows, which were shot into beseiged castles and towns.

Like many other devices, fire had advanced as a weapon in the twentieth century. The first modern flame thrower was invented in 1901, and was used by the Germans during World War I. It consisted of a pack containing a liquid agent worn by the soldier, a hose connected to the liquid agent, and a nozzle that measured the amount of liquid released. The liquid was squirted out of the hose and ignited by an attached spark device. The British army in World War II carried an effective flame thrower known as the Ack Pak that was capable of burning continuously for ten seconds. It was equipped with a cylinder of inert gas (usually nitrogen) that provided the pressure to propel petroleum gel a distance of 150 feet (46 m). A magnesium cartridge lit the fuel to produce the jet of flame. In addition, this device could shoot unlit fuel onto a target, which could be ignited later. The British also developed an armored vehicle with flame-throwing capability--the Crocodile. Its main gun remained intact, but the machine gun was replaced by a flame thrower that could shoot out to about 450 feet (137 m).

The flame-thrower does not seem to have been significant as a weapon after World War II. Its corollary might be napalm, a petroleum gel with an aluminum-based additive, that ignites when dropped from planes and burns even under water. It was used by the United States armed forces against North Korea and Vietnam.