Fact file: Units and formations

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The terms “unit” and “formation” are sometimes carelessly used interchangeably. Strictly speaking, the term “unit” and its derivatives apply to battalions and less and the term “formation” to brigades and above. The usefulness of the nomenclature lies in its use as a collective noun for similar-sized but differently named organisations, such as an infantry company, armoured squadron and artillery battery.
Units and formations are normally quadrangular, though it is customary to describe them as triangular. This derives from the sensible old custom of keeping a third of a force in reserve. For this reason, and to this day, units and formations therefore have three subordinate combat “building blocks”. The fourth constituency is generally a support element. For this reason, an infantry company consists of three rifle platoons and a support platoon or section and an artillery regiment of three cannon or rocket batteries and a support battery – although variations exist between corps and nations.           
US author James F Dunnigan observes that industrial-nation infantry battalions, on average have one vehicle for every eight to ten men, meaning over a 100 vehicles per unit. Of this number, a substantial number (20 to 60) will be supply trucks of various sizes and specialisations[1]. The strength of a brigade is usually 150-200 percent the infantry strength. “A brigade with three 700-man infantry battalions will often have a total manpower of 4200 troops.
In non-industrial states, unit and formation sizes tend to the smaller size and vehicles can be entirely absent.
Below follows a scematic representation of units and formations using terminology generally encountered in Commonwealth militaries, including South Africa’s.  
Generic
Approximate Size
Infantry
Armour
Artillery
Engineers
Formation
100,000-240,000
Numbered Army
Numbered Army
Formation
60,000
Corps
Corps
Corps
Formation
10,000-15,000
Division
Division
Division
Division
Formation
1500-5000
Brigade
Brigade
Brigade
Brigade
Unit
 
300-1000
Battalion
Regiment
Regiment
Regiment
Subunit
100-200
Company
Squadron
Battery
Squadron
Sub-subunit
 
30-40
Platoon
Troop
Troop
Troop
Sub-sub-subunit
 
8-14
Section
Section
Section
Section


[1] James F Dunnigan, How to Make War, A Comprehensive Guide to Modern Warfare in the 21st Century, 4th Edition, Quill, New York, 2003.