'The very existence of flamethrowers proves that some time, somewhere, someone said to themselves, "You know, I want to set those people over there on fire, but I'm just not close enough to get the job done." '
The earliest flamethrowers seem to have been syringe or syphon like devices for projecting greek fire. These were known in the ancient world and the Byzantines seem to have kept using them at least until the fall of Constantinople, after which they seem to have gone into abeyance - although a wide range of incendiary devices were used during the 1565 siege of Malta (and similar conflicts) and accounts vary as to whether or not and kind of fire-spray was included. The Chinese "Spear of Vehement Fire", despite being primarily a black powder based firework on a stick, may also qualify due to its flame-jet. The Chinese may also have deployed liquid spray flamethrowers from time to time.
In the modern era, experimental flamethrowers were developed for the War Between the States. Although they seem not to have been deployed in that conflict, from then on they began a slow return to prominence. Initially flamethrowers were ordnance class weapons, restricted largely to fixed mountings in fortifications until the German Army sucessfully deployed a man portable device (albiet with a two man crew) in the latter half of WW1. Defensive flamethrowers were, naturally enough, limited to defensive roles, mostly breaking up infantry attacks, although there seems to be some evidence of them being used as anti-shipping weapons to defend ports - which would almost count as a reversion to the fire-syphon armed galleys of Byzantium. The advent of the portable flamethrower allowed it to be carried forward with an infantry advance and used to reduce bunkers, pillboxes and similar fortifications.
This device was refined in the inter-war years and WW2 saw all nations deploying one-man portable units. These were employed throughout the war, but were quickly seen to have significant limitations - not least the volume of fire that the operator attracted from enemy troops eager not to be burned alive. Consequently a variety of vehicle mounted designs were developed, of which the most terrifying was almost certainly the Crocodile (A Churchill heavy tank mounting a flamethrower capable of throwing burning fuel out to close to 150 yards at the rate of several gallons a second). The USSR also developed a flamethrower designed to resemble a standard issue pack and rifle, but of course this was only effective until it fired, and even then the operator had to get uncomfortably close to the enemy.
A significant tactic developed duirng this period was the wet shot/dry shot combination - the operator could switch off the ingition system of this flamethrower and hose down the target with unlit fuel (a "wet shot"), hopefully saturating it without attracting too much attention. That fuel could then be ignited with a short burst of lit fuel (a "dry shot") or the use of an incendiary grenade or the like. This was not always viable - for example it lacked the same invasive effect on pillbox firing slits - but could be a lifesaver for the operator and increase the ability of the fuel to penetrate and ignite targets.
In the post war years use of flamethowers has declined - most developed world nations have de-issued them entirely by now and given their strongpoint reduction role to man portable shaped charge rounds and thermobaric weapons whilst using thermite/thermate based devices or white phosphorus in the incendiary role. An interesting exception to this was the Handflammpatrone DM34, issued by the Bundeswher as late as 2001 and consisting of a single shot, hand held flamethrower projecting a red phosphorous charge. In the modern era flamethrowers are generally civilian equipment used for large scale forestry work2.
Normally very badly represented in most games - especially videogames - where they are short ranged and largely ineffective.
Game and Story Use
- Most militaries don't need to fight monsters only vulnerable to fire - or swarms of small annoying creatures. Against either a flamethrower is probably a good bet.
- Flamethrowing was often used as a punishment detail in WW2 - at least partly because it was so dangerous.
- In the same vein, those who operate flamethowers should expect to be very unpopular with the enemy.
- These things were terrifying to face - those targetted with them would often surrender or run away even after an ineffective hit. Even more so when faced with something like the Crocodile. If your system allows for it, morale/fright checks would not be out of place.