Unified Ground Command

The Unified Ground Command (shortened as UNICOM) has control of all UNSC ground-based operations and is loosely modeled on the now-defunct United States Marine Corps. UniCom's roles include, but are not limited to, disaster relief, infantry operations, search and reconnaissance ops, and other "ground pounder" duties. Naval special warfare troops are an exception, and are instead controlled by Naval Command (NAVCOM).

Structure
The basic unit of the ground force operation is the squad, consisting of twelve soldiers, or thereabouts. Ground forces are further grouped into platoons, companies, battalions, regiments, and divisions. The force numbers given in the descriptions below are ideals, rarely matched exactly in the field. At the higher levels, these numbers include a significant amount of support personnel such as logistics and administration.

Fireteam
A Fireteam is the smallest unit. It contains a total of three soldiers plus a fireteam leader, usually a Lance Corporal or sometimes a Corporal.

Squad
A squad contains three fireteams, led by a Corporal or sometimes a Sergeant.

Platoon
A platoon normally contains three squads (thirty-nine men); plus the Platoon Leader, a Second or First Lieutenant; the Platoon Sergeant (the second-in-command), usually a Sergeant or Staff Sergeant; and a medic, for a total of forty-two men.

Company
A company contains four platoons, plus a group of personnel assigned as "Company Headquarters Section" (164 men in total), commanded by a Captain, with a Company First Sergeant. The twelve companies of a regiment are named phonetically "A" (Alpha) through "M" (Mike) with the exclusion of "J". First battalion consists of companies A through D, second battalion is companies E through H, and so forth.

A typical infantry company would have three infantry platoons and one heavy weapons platoon, but these numbers are flexible depending on the unit type and mission. T companies, for example, eschew this model and mix their heavy weapons personnel into each platoon, so all the platoons have one heavy weapon squad.

Battalion
A battalion contains four companies, plus a group of command and staff personnel assigned as Headquarters Company;(eight hundred men in total), commanded by a Lieutenant Colonel, with a Battalion Sergeant Major; a Sergeant Major in the Marines or a Command Sergeant Major in the Army.

Regiment
A regiment contains three battalions, plus a group of personnel assigned as Headquarters Company (three thousand men in total), commanded by a Colonel with a Sergeant Major.

Division
A division contains four regiments, plus a group of personnel assigned as Headquarters Battalion (fourteen thousand men in total), commanded by a Major General. The extra personnel in the force number given are support units, including medical, combat engineering, maintenance, and military police.