Unggoy Heavy

Gunner Grunt is a Covenant Unggoy (Grunt) rank.

Place in Grunt ranking system
It is currently unknown if Gunner Grunts are an actual rank, or maybe just a sub class. Though slightly stronger then Minor Grunts, they seem to be weaker the Major Grunts. This may mean that it is actually in-between the two ranks, but this remain a speculation.

Armor
Gunner Grunts wear distinctive green armor with methane breathers, but are otherwise similar to other Grunts in terms of armor style.

Combat
Gunner Grunts are usually seen in conjunction with other Covenant infantry, and most often operate a Plasma Cannon, hence their name. However, sometimes, they will wield a Fuel Rod Gun.

They usually will not flee from their position until 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 easy to kill with any method you use, though their armor seems to be tougher than the average Grunt's. Most likely to protect them from explosives from their Fuel Rod Gun.

Note that the cannon is free for you to use after taking out its operator. However, the Gunner Grunt must deploy a cannon on a tripod before operating it, and if killed before deploying a cannon, the cannon is inoperable.

Appearances
Gunner Grunts have only been seen in Halo 2:

On the level Gravemind, several Gunner Grunts are deployed to take out the Master Chief
 * Cairo Station - two Gunner Grunts man Plasma Cannons at Hangar A-02
 * Delta Halo - a handful of Gunner Grunts man Shielded Plasma Cannons at the beginning of the level, defending against an attack by SPARTAN-117 and Orbital Drop Shock Troopers.