M4 Napalm Adherent Weapon

The M4 Napalm Adherent Weapon (more formally, Flame Projector, Fuel Adherent, Model 4), marketed by Weapon System Technologies as the NA4 Flamethrower, is a man-portable backpack flamethrower in use with the United Nations Space Command Defence Force. Despite its name, the M4 does not project a stream of napalm, instead making use of the similar though more destructive Pyrosene-V.

History
The M4 was first developed by Weapon System Technologies for the UNSC during the assault phase of Operation: TREBUCHET: UNSC troops battling URF forces at the Washington Line on Eridanus II found that small arms were mostly ineffective against the rebel defenders and made extensive use of high explosives and hand grenades to flush the rebels out of bunkers. The UNSC High Command recognised that the rate of explosives use was unacceptable and commissioned WST to develop a new flamethrower that could be used against rebel forces.

The M4 was effectively used by UNSC forces in putting down rebel resistance, but its effects were so horrific that the Eridanus National Party made an official complaint in Parliament against its use, and nearly three million citizens signed a petition against its use, though to no avail. Even among UNSC forces, flamethrower operators, nicknamed "Hellbringers", were looked upon with a mixture of awe and revulsion.

With the outbreak of the First Great War, however, the M4 flamethrower gained acceptance among UNSC troops: It saw extensive use during the Harvest Campaign, since it was one of the few available weapons that could kill Covenant troops in bunkers. However, there were a great deal of casualties among Hellbringers to to the extreme danger of engaging a bunker at close range, and also because Covenant plasma weapons could easily pierce the fuel tanks and ignite the Pyrosene-V (contrary to popular belief, UNSC forces faced no similar dangers against bullets or shrapnel; see below). After large numbers of M67 TBNE rockets for the M41 Medium Anti-Vehicle/Assault Weapon were developed, allowing for a greater engagement range against bunkers and a more lethal effect, the M4 was removed from front line service and was pressed into use as an engineering weapon along with the M7057/Defoliant Projector. However, it still saw some use as an emergency weapon in the last years of the First Great War, the War of Vengeance, and the Second Great War.

Design
The M4 consists of three large backpack tanks linked to a large projector system. Two of the tanks contain 7.57 litres each of Pyrosene-V, a fuel gel mix that can adhere to a target. Its effects are similar to that of napalm-treated gasoline, giving rise to the weapon's name, but instead of the gasoline, polystyrene, and benzene mixture used in napalm, Pyrosene-V is a kerosene-based fuel with a lower concentration of benzene. It has has less impact on the environment than napalm, and also contains an oxidizing agent, making it more difficult to put out once ignited. Pyrosene-V burns at nearly 2500 degrees Celsius and has a burn time of around sixty seconds. The third tank is filled with inert nitrogen gas, used as a propellant. In addition, the weapon can use a wide range of flammable fuels to compensate for the variety of atmospheric and gravitational conditions it might be used in.

Contrary to popular belief, flamethrower operators do not face a fiery death if the tank is hit by sparks, shrapnel, or bullets. Nitrogen is a non-flammable gas that is stored under high pressure. Should the nitrogen tank be ruptured, it might knock the operator forward as the gas bursts out. The Pyrosene-V in the fuel containers is actually exceptionally difficult to light, which is why magnesium-filled igniters are used when the weapon is fired. Should the tank be hit, the mixture will simply leak out unless the round is an explosive or incendiary type that could possibly ignite the mixture inside. Plasma weapons, however, will nearly always cause the mixture to ignite on impact.

When the M4's trigger is pulled, the nitrogen propels the liquid fuel out of the cylinder through a flexible pipe and then into the large gun element of the M4 system. The gun consists of a small reservoir, a spring-loaded valve, and an ignition system; pressing a trigger opens the valve, allowing pressurized flammable liquid to flow and pass over the igniter and out of the gun nozzle. The igniter works on a magnesium-based system to ignite the Pyrosene-V. The firing safety catch is at the back of the rear grip. At the front of the rear grip is the firing trigger. On top of the upper front grip is the igniter safety catch and the igniter trigger. The ignited fuel stream can be bounced off walls and ceilings to project the fire into blind and unseen spaces. Alternatively, an unignited stream of fuel can be fired and afterwards ignited, possibly by a lamp inside the bunker or second flame shot. Unlike other flamethrowers, the M4 mounts Picatinny Combat Attachment Points on all four sides, allowing for the attachment of optics, aiming modules, and ancillary weapons such as the M301 Grenade Launcher.