This week I finished another support team for my US forces in Chain of Command. The M2 Flamethrower is both a terrible and terribly effective weapon when used against fixed fortified positions like bunkers or pillboxes. Its effectiveness is all the more surprising given that the US didn't start the war with any flamethrower weapons in its arsenal. Instead, they threw together a temporary weapon (it took just 90 days to go from design phase to production), but even before it was issued to troops, plans were already afoot to build its successor. The Army then went out and acquired examples of German, French and British equipment and designed something better ('better' is a matter of perspective, given these are designed to burn people to death!).
The resulting weapon, the M2 went into production in early 1944 and saw service through the rest of WW2, into Korea (where it became the M2A1) and even saw service in Vietnam. When filled, it weighed 70lb and held 4.75 gallons of fuel providing about 6-7 seconds of firing time. When using liquid fuel it's effective range was about 20 yards, but when filled with a gelled fuel (napalm basically) its range was doubled to 40 yards.
The unit is made up of a backpack and a gun attached by a pressurised hose. The backpack consists of three tanks. The two larger ones contain the fuel (filled from the valves at the top) while the smaller tank contained compressed Nitrogen at 1500psi which pressurised the whole system to about 300psi via a regulator valve at the bottom. If the valve failed for any reason, there was a pressure release valve, which in the M2 consisted of a small valve and tube assembly on top of one of the fuel tanks. The later M2A1 moved this to a less exposed location at the bottom of the unit but both versions were designed to release pressure (and fuel) safely away from the operator. The harness also had a quick release buckle so the unit could be dumped quickly in an emergency.
The Gun part of the unit was connected to the tanks by a multi-layered high-pressure hose. The Gun itself consisted of two triggers. The rear one was a handle grip trigger that realised the pressurised fuel into the gun and opened the valve at the front allowing the fuel to be released towards the target. The Forward trigger (which looks like a regular trigger) ignited the fuel. Hollywood flamethrowers often have electrical arcs igniting the fuel but these don't work very well in damp conditions and not at all when the battery dies. The M2, however, used a cartridge of five mini flares, each of which would burn for a few seconds. This means the operator had a maximum of 5 'shots' with the M2 with a combined maximum of 6-7 seconds of fuel capacity.
Later in the war, the use of armoured flamethrowers like the Crocodile made the use of man-packed weapons less prevalent in Europe, however, they continued to be effective in Jungle fighting against the Japanese. Eventually, all flamethrowers (indeed the use of all incendiaries against people) were banned by Protocol III of the Geneva Convention, but this did not come into effect until 2005! As I said earlier a terrible weapon, but also a terribly effective one which is why pretty much everyone had variations of these in their arsenals.