Corps

In military terminology from the twentieth century forward, the corps has been the highest-level military headquarters that has a purely tactical, as opposed to tactical and support/administrative role. In NATO terminology, a corps was an ad hoc unit consisting of two or more divisions (i.e., standing organizations of 10,000-25,000 soldiers each) plus significant corps-controlled attached units).

Less commonly, corps refers not to a specific tactical organization, but a type of military function such as "medical corps", "corps of engineers", or "tank corps". This meaning is generally synonymous with "branch" or sometimes "department".

Functional meaning

This usage may refer to a unit that provides a service as well as the career management path for personnel with that function. In the British Army, the Royal Logistics Corps is both the largest corps organization, but also the staff function that oversees the careers of logistics personnel.

In contrast, the U.S. has three corps concerned with logistics, Quartermaster (i.e., supply), Ordnance (i.e., weapons maintenance and technical support) and Transportation. Transportation Corps personnel are trained through their branch, and transportation doctrine comes from the branch headquarters, but units such as a Transportation Truck Company are part of a combined arms unit.

Organizational definition

Some national militaries use "corps" as a level of geographic organization. For example, the Republic of Vietnam (South Vietnam) had four corps, I Corps in the northernmost part of the country, III corps near the capital, etc. To avoid confusion, U.S. corps-sized units operating in Vietnam were called "field forces". Field forces were tactical headquarters.

In the U.S. military, a corps is also called a unit of employment, which is an administrative and headquarters organization that controls tactical units of action, which may be Brigade combat teams or divisions.

Equivalents

Not all militaries, even of large size, used the term "corps". In the Second World War, Japan's equivalent of a corps-sized organization was an "army", and the equivalent to a Western army was an "area army".

The Soviet Union often went from division to army; a Soviet army was often the size of a Western corps. On occasion, the Soviets would create a corps headquarters, usually for a specific purpose.