Infantry units

Militaries have traditional names for the size of units they field. The names can be ambiguous, and there is considerable overlap.

In general the largest unit in a nation's army is called an army, although, during World War 2, some nations referred to their largest units as "army groups". Armies are sometimes, but not always, composed of at least two "corps". A corps is further composed of "divisions." A division is further composed of either "brigades", "regiments", or "battalions". Brigades and regiments, if they are present, are composed of battalions.

Infantry battalions are usually composed of "companies". Infantry companies are composed of "platoons". Finally, platoons are composed of "squads".

A brigade is the smallest unit commanded by a general, a brigadier. Regiments are commanded by a full Colonel, while a battalion is commanded by a Colonel or Lieutenant Colonel. Companies are commanded by a Major of Captain. A platoon is commanded by a Lieutenant, while squads are commanded by non-commissioned officers.

The size of infantry units is also ambiguous. However, a squad is, generally, about a dozen soldiers. A battalion is, generally, 500 to 1000 soldiers. A division is, generally, 10-20 thousand soldiers.

The companies in the armies of ancient Rome were called centuries because they contained about 100 soldiers. A Roman legion contained about 10 thousand soldiers, making it roughly equivalent to a modern division.