M7057 flamethrower

The M7057 Defoliant Projector Flamethrower is a special weapon only available in the Halo PC/Mac Multiplayer versions of the game. Though it was meant to be featured in the Halo: Combat Evolved Campaign and Halo 2, it did not make it into either game.

Advantages
The Flamethrower can kill an enemy very quickly if used in close proximity, and the enemy continues to burn after they are hit with the flamethrower, sometimes causing them to die even if they run away. It is also stingy when using up fuel units, so protracted blasts of flame are sustainable on one fuel container. Finally, there is no need for accuracy when using the Flamethrower; merely pointing it in the enemy's direction will kill them in seconds. Also, the flamethrower has a capability of being unlimited in the first multiplayer map. The flamethrower is very effective against any campaign unit. You can only fight against campaign units with multiplayer weapons by modding.

Disadvantages
Several things counterbalance the Flamethrower's high damage rate. First of, it reloads slowly, and is subject to overheating. Second, ammunition is often unavailable. And third, the Flamethrower can damage its own user if one walks into the trail of flame left behind by the weapon. This lets the enemy run away while stopping the user from giving chase. If used at a distance, the Flamethrower takes longer to kill an enemy, and might not even damage them. Finally, the Flamethrower is very rare. There are only one or two of them per map. Moving also affects the damage put out by the flamethrower. If you move forward while firing, the flame will be more damaging, but when moving backwards, the flame does about the same as an assault rifle. Therefore, while using this weapon in combat, your movement options are limited.

Influences
The Defoliant Projector Flamethrower was inspired by a similar flamethrower from the Marathon series. The shark-like decal on it is borrowed from the game as well. In Marathon, however, it is featured on the rocket launcher. The Defoliant Projector's number, 7057, is a alpha-numeric callback to the Weapon from Marathon's name, the TOZT. There is also a high chance it was influenced by the flamethrower from the Aliens movies, as was the assault rifle.

Multiplayer Role
Using the Flamethrower in small spaces or in groups of enemies works best, and the trail of flame blinds snipers by producing a temporary smokescreen. It is especially effective if used to retreat by running backwards away from an enemy to leave a trail of flame, deterring would-be pursuers from giving chase to a wall of fire. This weapon can also take out groups of people in vehicles, provided they are close and moving relatively slowly. Effective uses include infiltrating an enemy base and defending the flag in CTF. It is also a very good ambush weapon, as it does a lot of damage in a short amount of time.

Trivia
The Flamethrower's number designation,7057, can be translated from "number speak", and it means the TOST. It may be a reference to the Marathon Flame Thrower, which was named the TOZT-7, or it simply relates to the flamethrower's function, to toast things.

In the cutscene of the level Keyes, where the Master Chief retrieves Captain Keyes' neural implants, the Master Chief was meant to burn Keyes' skull out of the Brain Form and retrieve the implants. However the final skull was said to be too gruesome to put into the game, so the flamethrower was removed.

It might appear in Halo 3 as a Power Weapon, like the new Chain gun, a weapon that could be extremely lethal at close range, and might out do the Shotgun or Sword due to the burning after affect on foes. This theory of it being included is supported by an EGM article on Halo 3 Multiplayer that you could affect player appearances based on performance, such as "Making them look like they are on fire." Also, the Chain Gun was an early concept from Halo, but was cut during development. The Flamethrower may make one last appearance in the finale to the Halo trilogy, just for the sake of including it.