Phoenix Logs/UNSC Units/Hellbringers
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Anti-infantry Marines armed with flamethrowers.
Each Hellbringer carries a heavy flamethrower which deals area of effect damage against close range targets. The flamethrower is very effective against infantry - even those garrisoned in structures - but is of limited use against armored vehicles. The flamethrower can be upgraded with dispersion nozzles that increase damage and size of the flame sheets.
Marines willing to strap a tank of volatile chemicals to their back to fire a jet of superheated flame at enemies are braver [and crazier] than most. Though the UNSC adopted thermobaric munitions for deploying most incendiaries, the liquid projector flamethrower proved its worth to the Spirit of Fire's combat teams by burning out dug-in Covenant infantry, sterilizing Flood infestations, and heating up decades-old MREs.