Army (unit)

Military organization
Typical units	Typical numbers	Typical commander
fireteam	3–4	corporal
squad/ section	8–12	sergeant
platoon	15–30	lieutenant
company	80–150	captain/major
battalion/ cohort	300–800	lieutenant colonel
regiment/ brigade	2,000–4,000	colonel/ brigadier general
division/ legion	10,000–15,000	major general
corps	20,000–40,000	lieutenant general
field army	80,000+	general
army group	2+ field armies	field marshal/ five-star general
region/ theater	4+ army groups	Six-star rank/Head of state

Common military ranks in English
Navies	Armies	Air forces
Commissioned and Non-commissioned officers
Admiral of the fleet	Marshal or Field marshal	Marshal of the air force
Admiral	General	Air chief marshal
Vice admiral	Lieutenant general	Air marshal
Rear admiral	Major general	Air vice-marshal
Commodore	Brigadier or Brigadier general	Air commodore
Captain	Colonel	Group captain
Commander	Lieutenant colonel	Wing commander
Lieutenant commander	Major or Commandant	Squadron leader
Lieutenant	Captain	Flight lieutenant
Sub-lieutenant	Lieutenant or First lieutenant	Flying officer
Ensign	Second lieutenant	Pilot officer
Midshipman	Officer cadet	Flight cadet
Enlisted grades
Warrant officer or Chief petty officer	Warrant officer or Sergeant major	Warrant officer
Petty officer	Sergeant	Sergeant
Leading seaman	Corporal	Corporal
Seaman	Private	Aircraftman

A field army (or numbered army or simply army) is a military formation in many armed forces, composed of two or more corps and may be subordinate to an army group. Likewise, air armies are equivalent formation within some air forces. A field army is composed of 100,000 to 150,000 troops.

Particular field armies are usually named or numbered to distinguish them from "army" in the sense of an entire national land military force. In English, the typical style for naming field armies is word numbers, such as "First Army"; whereas corps are usually distinguished by Roman numerals (e.g. I Corps) and subordinate formations with ordinal numbers (e.g. 1st Division). A field army may be given a geographical name in addition to or as an alternative to a numerical name, such as the British Army of the Rhine, Army of the Niemen or Aegean Army (also known as the Fourth Army).

The Roman army was among the first to feature a formal field army, in the sense of a very large, combined arms formation, namely the sacer comitatus, which may be translated literally as "sacred escort". The term is derived from the fact that they were commanded by Roman emperors (who were regarded as sacred), when they acted as field commanders. While the Roman comitatensis (plural: comitatenses) is sometimes translated as "field army", it may also be translated as the more generic "field force" or "mobile force" (as opposed to limitanei or garrison units).

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Wikipedia