The M2 flamethrower utilised by Allied forces during WWII proved to be a devastatingly effective weapon against bunkers -- and Axis psyches. However, walking around a firefight with a napalm-filled backpack and an effective range of 20 metres is a great way to become a crispy critter. So the US military developed the M202 FLASH rocket-propelled flamethrower.
The M202A1 FLame Assault SHoulder weapon (FLASH) is a four-shot rocket launcher armed with incendiary M74 rockets. It is designed to perform the same function as the M2, only better. The FLASH boasts five times the range of conventional flame throwers at only half the weight. It's also extremely accurate, capable of lobbing a rocket through bunker ports, machine gun nests, foxholes and into other fortified positions up to 750 metres away. The system is capable of firing rockets individually, at a rate of one per second, or all four simultaneously. The FLASH's four M74 66mm rounds are loaded with a M235 Incendiary warhead packed with over a pound of TPA each. TPA -- thickened pyrophoric agent -- is like napalm, only better.
Made from triethylaluminum and polyisobutylene, TPA is nasty stuff. When exposed to air, the triethylaluminum spontaneously combusts and burns at a white hot 1200C. That's hot enough to burn people, unarmored vehicles, buildings, bunkers and anything else unlucky enough to be within the M74's 20m blast radius. As such, the M202 proves quite effective at suppressing everything from advancing troops to RPG sites to armoured vehicles -- without putting the operator in the line of fire.
While the M202 significantly outperforms its predecessor, the FLASH is not without its own shortcomings. Only one 12kg, 60cm long launcher was assigned to each rifle platoon. This meant that one member had to carry it as well as his rifle. In addition, the ammo itself had a nasty habit of setting itself off when being loaded. Due to these drawbacks, the M202 has generally wasted away in armories since the mid 1980s. Although the FLASH has been carried by troops in the latest conflicts in Iraq and Afghanistan.