The Unified Ground Command (shortened as UNICOM) has control of all UNSC ground-based operations and is loosely modelled 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 NAVCOM.
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.
A company contains four platoons, plus a group of personnel assigned as "Company Headquarters Section" (164 men in total), commanded by a First Lieutenant or Captain, with a "Company Sergeant", usually a Staff Sergeant or a Gunnery 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.
A battalion contains four companies, plus a group of personnel assigned as "Battalion Headquarters Section" (eight hundred men in total), commanded by a Major or Lieutenant Colonel, with a "Battalion First Sergeant, "usually a Gunnery Sergeant or above.
A regiment contains three battalions, plus a group of personnel assigned as "Regimental Headquarters Section" (three thousand men in total), commanded by a Colonel, or in some cases a Brigadier General.
A division contains three regiments, plus a group of personnel assigned as "Division Headquarters Section" (fourteen thousand men in total), commanded by a Brigadier General or Major General. The extra personnel in the force number given are support units, including medical, combat engineering, maintenance, and military police.