Unggoy Heavy

Heavy Grunt is a Covenant Unggoy rank equivalent to the UNSC Corporal. This rank is designated for use of heavy weapons and turrets.

Armor
Heavy Grunts wear distinctive emerald-greenish armor with a methane breather, but are otherwise similar to other Grunts in terms of armor style. They can take much more damage than Grunt Minors and Majors, but not as much as higher ranking Grunt Ultras and SpecOps Grunts.

Combat
Heavy Grunts are usually seen in conjunction with other Covenant infantry, operating as heavy support units, and usually operate heavy weapon systems such as Plasma Cannons, Shade Turrets, and Fuel Rod Guns with deadly effect.

They will usually not flee from their position unless the player is too close or out of range of their weapon, in which case they will pull out a Plasma Pistol and attack like a normal Grunt. They are easily dispatched using most tactics, though their armor seems to be tougher than the average Grunt, most likely to protect them from explosives and other heavy weapons fire. Unlike most Grunts, they will rarely throw Plasma Grenades.

Note that the cannon is free for you to use after taking out its operator. In Halo 2 a Heavy Grunt must first deploy its Plasma Cannon before it can be used. If the Grunt Heavy carrying the Plasma Cannon is killed before it can deploy it then it cannot be used. This is not the case in Halo 3 since most of the Plasma Cannons encountered are already deployed with the exception of few, and can still be used even if they are detached from their tripod.

In Halo 3, Heavy Grunts are seen utilizing many different heavy weapons and vehicles. They are commonly seen driving Ghosts, and seem to be very skilled drivers, especially on higher difficulties. Grunts will attempt to ram enemies and will keep their distance from advancing foes. Heavies may also work in teams on higher difficulties, where one rams a foe and another shoots the foe out of what they are driving. Usually if they're not piloting a Ghost then they're manning a turret or carrying a Fuel Rod Gun. Like SpecOps and Ultra grunts, they are some of the more dangerous and tactical Unggoy. When not manning a vehicle or turret or carrying a Fuel Rod Gun, Grunt Heavies will usually use Plasma Pistols, but on higher difficulties they may use Needlers. They are very efficient with these weapons, even overcharging them which is uncommon among most Unggoy.

On the Heroic and Legendary difficulty settings where their heavy weapons can make short work of the player, their lethal efficiency with anything they use has coined the term "Green Grunts are Horrible People"; a widely used term on Xbox Live.

Trivia

 * Heavy Grunts are rarely seen wielding Spikers. This is easier to find when the player destroys a Phantom, the Grunt will most likely (if it survived) be wielding a Spiker.
 * The only time a non-Heavy Grunt is seen deploying a Plasma Cannon is in Halo 2 at the beginning of the level The Arbiter, where a Spec Ops Grunt is seen carrying one. This is because the only Unggoy allies encountered in the level are Special Operations Grunts and one Ultra Grunt.