A military unit is an organisation within an armed force. It may consist of any number of soldiers, ships, vehicles, or aircraft. Armies, navies, and air forces, are organised hierarchically into groups of various sizes for functional, tactical and administrative purposes.
Technically, a unit is a homogenous military organisation, such as a battalion (infantry), or regiment (cavalry), and its administrative and command functions are considered to be at the unit level. Smaller organisations (companies, platoons, sections), are minor units, as opposed to battalions and regiments, which are major units.
Larger military organisations (brigades and higher) are formations. A formation is a collection of separate units, each with their own command structures.
The specific composition of a military organisation is sometimes called an "Order of Battle" or Orbat for short.
Hierarchy of military organisation
This article gives an overview of some of the terms used to describe military units in armed forces across the world. Whilst it is recognised that there will be differences between armies of different nations, it seems that a large proportion are modelled on the British and/or American models. Readers interested in the detailed specifics of a national army (including the British and American) should consult the relevant entry for that country.
Rungs may be skipped in this ladder: the UK merges the regiment and brigade under the term "brigade" and calls the battalion a regiment in some arms, for example. Likewise, only large military powers consider the top levels (today, Canada starts at the division level, for example).
Army, army group and theatre are all large formations which vary significantly between armed forces in size and hierarchy position.
Different arms and countries may also use traditional names, creating considerable confusion: for example, a British or Canadian armoured regiment (battalion) is divided into squadrons (companies) and troops (platoons), whereas an American cavalry squadron (battalion) is divided into troops (companies) and platoons.