Unggoy combat harness

The Unggoy combat harness is a type of body armor and environmental suit issued to the Covenant's Unggoy warriors. It provides basic protection from hostile fire and the elements and is also equipped with a breathing apparatus for the Unggoy.

Breathing apparatus
The gas is stored in extremely cold tanks inside the suit, and is provided to the user through a breathing mask that covers over half of the alien's head. The backpack attached to a Grunt's back contains a methane tank. Attached to every Grunt's wrist is a readout (measured in Covenant units) of the amount of methane left in the Grunt's pack. When the tank gets low, a resupply of methane must be found quickly or the Grunt will suffocate. The suit also displays the color of the Grunt's rank. The breathing mask of the Unggoy also makes speech difficult for them, as it muffles their words.

Defense
In addition to its life support role, it is equipped with armor. This armor can withstand limited amounts of fire, especially from energy weapons. The M6D is capable of easily cracking through the armor and is considered by some to be the standard weapon for such actions. The armor piercing rounds of the Assault Rifle are also potent weapons against the harness. As well as defending against projectiles and plasma, it prevents a limited amount of fall damage to its user, like its Sangheili counterpart. Despite this, most variants are vastly inferior to the other types of armor adorned and used by the Covenant, no doubt due to the costs required to produce the suits for the extremely large population of Unggoy soldiers. Some variants are also equipped with helmets, active camouflage and a methane-filled breathing apparatus.

Appearance
The visual appearance of the Unggoy combat harness has changed considerably every time it has appeared in fiction; this has led to confusion as to whether or not these are separate variants or if the differences are simply aesthetic in nature.

In Halo: Combat Evolved, there was a variant with a partially curled-back methane tank, along with a larger methane rebreather. This variant is commonly referred to by fans as "curl-backs". This variant is absent in newer titles. In Halo Wars, the combat harness used by Ripa 'Moramee's Suicide Grunts use cylinder-like methane tanks and goggle-like rebreathers. In Halo: Reach, the design of the harness varies greatly between different Unggoy ranks. Along with the traditional combat harness, which is now worn exclusively by Unggoy Minors.

The first variant is a two-pronged methane tank used by both Unggoy Majors and Special Operations Unggoy.

The second variant is features a cylindrical methane tank that is worn by Heavies and Ultras. While visually similar to the ones used by Halo Wars' Suicide Grunts, it is still otherwise a different variant.

Unggoy Heavies, Special Operations Unggoy and Unggoy Ultras wear rebreathers that fully cover their faces (the Ultras wear actual helmets). Unggoy Ultra helmets offer more protection than normal masks, capable of blocking an entire headshot before falling off.

In Halo 4, at least one non-standard combat harness model have been drastically altered. The armor is much more minimalistic, barely covering the Unggoy's torso. The new skullcap helmet delivers methane directly to the wearer's nostrils, removing the need for the obstructive rebreathers present in older models. This allow Unggoy soldiers to be more expressive in combat. It is currently unknown whether standard harnesses have underwent similar changes.

Trivia

 * In Halo 3, Halo 3: ODST, and Halo: Reach the methane mask can be knocked off. However the Grunt will continue fighting despite its sudden lack of a methane source.
 * There appears to be no visible way for the methane to reach the Grunt's mouth, since the mask and the air tank are completely unconnected. It has been theorized that the methane is transported to the mask through slipspace, which has been hinted to be used in smaller Covenant devices such as in their weaponry.