The military use of flamethrowers is restricted through the Protocol on Incendiary Weapons.
The flamethrower's effective range is short in comparison with that of other battlefield weapons of similar size. To be effective, flamethrower soldiers must approach their target, risking exposure to enemy fire. Vehicular flamethrowers also have this problem; they may have considerably greater range than a man-portable flamethrower, but their range is still short compared with that of other infantry weapons.
A propane-operated flamethrower is a straightforward device. The gas is expelled through the gun assembly by its own pressure and is ignited at the exit of the barrel through piezo ignition.
The British World War II army flamethrowers, "Ack Packs", had a doughnut-shaped fuel tank with a small spherical pressurizer gas tank in the middle. As a result, some troops nicknamed them "lifebuoys". It was officially known as Flamethrower, Portable, No 2.
In the Pacific theatre, the U.S. Army used M-1 and M-2 flamethrowers to clear stubborn Japanese resistance from prepared defenses, caves, and trenches. Starting in New Guinea, through the closing stages on Guadalcanal and during the approach to and reconquest of the Philippines and then through the Okinawa campaign, the Army deployed hand-held, man-portable units.
Often flamethrower teams were made up of combat engineer units, later with troops of the chemical warfare service. The Army fielded more flamethrower units than the Marine Corps, and the Army's Chemical Warfare Service pioneered tank mounted flamethrowers on Sherman tanks (CWS-POA H-4). All the flamethrower tanks on Okinawa belonged to the 713th Provisional Tank Battalion. It was tasked with supporting all U.S. Army and Marine infantry. All Pacific mechanized flamethrower units were trained by Seabee specialists with Col. Unmacht's CWS Flamethrower Group in Hawaii.
In cases where the Japanese were entrenched in deep caves, the flames often consumed the available oxygen, suffocating the occupants. Many Japanese troops interviewed post war said they were terrified more by flamethrowers than any other American weapon. Flamethrower operators were often the first U.S. troops targeted.
USA army flamethrowers developed up to the M9 model. In the M9 the propellant tank is a sphere below the left fuel tank and does not project backwards.
A squad armed with backpack flamethrowers had an important part in the 2012 Summer Paralympics closing ceremony. They had one big tank each. They could make a flame about 12 feet (3.7 m) long.
It has been known for police to fill a "flamethrower", not with flammable liquid, but rather with tear gas dissolved in water as a riot-control device; see Converted Flamethrower 40.