Unggoy Heavy

Gunner is a Covenant Unggoy (Grunt) rank.

Rank
It's as of yet unknown where a Gunner stands in the Grunt ranks. They seem to still attack you if you get to close to fire at with their Plasma Cannon, which may signify being a Major. This, however, is pure speculation.

Armor
Gunners wear distinctive green methane breathers, but are otherwise similar to his brethren.

Combat
Gunner Grunts are usually seen in conjunction with other Covenant infantry, and most often operate a Plasma Cannon, but sometimes 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. Note the cannon is free for you to use after taking out its operater.

Appearances
Gunners have only been seen in Halo 2. There most obvious locations are in Hangar A-02 on the Cairo and at the beginning of Delta Halo.