Unggoy Heavy

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

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 are usually operating 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. Their armor seems to be slightly tougher than the average Grunt, most likely to protect them from explosives and possible backfiring of their powerful weapons. Unlike most Grunts, it is strangely rare for Heavy Grunts to throw Plasma Grenades.

Note that the cannon is free for a player 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. They 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 skillful drivers, especially on higher difficulties. Grunts will attempt to ram enemies and will keep their distance from advancing foes. Heavy Grunts may also work in teams on higher difficulties in which case 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 Spec Ops 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 firing rapidly enough to create a super detonation which is uncommon among most.

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". This is a widely used term on Xbox Live.

Appearances
Heavy Grunts do not appear in Halo: Combat Evolved at all. However, they have been seen in several levels of Halo 2, Halo 3 and Halo 3 ODST

Halo 2

 * Cairo Station - Two Heavy Grunts at Hangar A-02 and three at Commons B-01 man Plasma Cannons.
 * Outskirts - Three Heavy Grunts are found manning plasma cannons in the tunnel.
 * Delta Halo - Four Heavy Grunts man Shielded Plasma Cannons at the beginning of the level, defending against attack by SPARTAN-117 and Orbital Drop Shock Troopers.
 * Gravemind - Several Heavy Grunts are deployed to take out the Master Chief, all are equipped with deadly Fuel Rod Guns, except for the two Gunners at the start of the level. You can find them also when your at the second grav-lift that takes you across, not up, supporting three Spec Ops Elites.

Halo 3

 * The Storm - Seen on the Scarab on higher difficulties manning plasma turrets and on the last part of The Storm carrying a plasma turret which it will set up when his comrades see you when you go to take out the Covenant AA gun. They are also seen piloting the Ghosts dropped off by the Phantom to give support to the AA Wraith.
 * The Ark - Seen in many points throughout the level, they drive many of the light vehicles and operate plasma cannons from many positions, including two atop a Gravity Platform in the beginning area. There are also two with Fuel Rod Guns half way into the level, and at least one with a Brute Spiker.
 * The Covenant - Depending on the difficulty, two Heavy Grunts armed with Fuel Rod Guns defend each of the hallways that lead to the Prophet of Truth. The first area in the hallway, on Legendary, three heavies, two with a fuel rod, the other with a turret will arrive as reinforcements. In the next hall, two of them are fighting with the Brutes. They both wield Fuel Rod Guns. They are also seen in the beginning of the level defending the first tower.
 * Most Shades in Halo 3 are operated by Heavy Grunts, appearing in most levels. Ones not operated by Heavy Grunts are operated by Grunt Minors.
 * In every level (excluding The Covenant) Heavy Grunts are seen operating the plasma cannons on enemy Phantoms.

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 or a Mauler.
 * 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.
 * Heavy Grunts are classified as Grunt Spec ops in Firefight, where white armored grunts are simply classed as regular grunts. Spec op grunts in Firefight are only seen manning the side mounted plasma turrets on the phantoms.