A flamethrower is a ranged incendiary device designed to project a controllable jet of fire. First deployed by the Byzantine Empire in the 7th century AD, flamethrowers saw use in modern times during World War I, and more widely in World War II as a tactical weapon against fortifications.
Most military flamethrowers use liquid fuel, typically either gasoline or diesel, but commercial flamethrowers are generally blowtorches using gaseous fuels such as propane; gases are safer in peacetime applications, because their flames have less mass flow rate and dissipate faster, and often are easier to extinguish when necessary.
The military use of flamethrowers is restricted through the Protocol on Incendiary Weapons.
Apart from the military applications, flamethrowers have peacetime applications where there is a need for controlled burning, such as in sugarcane harvesting and other land-management tasks. Various forms are designed for an operator to carry, while others are mounted on vehicles.
Modern flamethrowers were first used during the trench warfare conditions of World War I and their use greatly increased in World War II. They can be vehicle-mounted, as on a tank, or man-portable.
The man-portable flamethrower consists of two elements—the backpack and the gun. The backpack element usually consists of two or three cylinders. In a two-cylinder system, one cylinder holds compressed, inert propellant gas (usually nitrogen), and the other holds flammable liquid, typically some form of petrochemical. A three-cylinder system often has two outer cylinders of flammable liquid and a central cylinder of propellant gas to maintain the balance of the soldier carrying it. The gas propels the liquid fuel out of the cylinder through a flexible pipe and then into the gun element of the flamethrower system. The gun consists of a small reservoir, a spring-loaded valve, and an ignition system; depressing a trigger opens the valve, allowing pressurized flammable liquid to flow and pass over the igniter and out of the gun nozzle.