After a dismal first attempt at designing a flamethrower (the M1) in 1941, the US Chemical Corps along with several universities and industrial partners put in a lot of research to develop a more usable and effective flamethrower. The result was the M2, which went into production in early 1944. It would prove to be an exceptionally effective weapon in the island-hopping campaign towards the end of the war.
The M2 was arguably the best flamethrower fielded by any military during the war, with a number of excellent design features. These included:A constant-pressure regulator to ensure that the range stayed the same from the first to the last shot of a tank of fuel An on/off main valve easily accessible to the operator A supremely waterproof and reliable pyrotechnic cartridge ignition system An auto-shutoff valve which sealed at the nozzle, preventing dribble (and cutting off fuel flow should the operator lose control of the weapon)
The M2 would see service into the Vietnam War even as its successor the M9 was being issued. It was a truly outstanding design, and remains viable to this day.
Thanks to Charlie Hobson for showing us the unit and teaching me to fire it, and also thanks to Adaptive Firearms for letting us use their range facilities!
You can find Charlie Hobson's book, "US Portable Flamethrowers" here: http://amzn.to/1SP9yc5