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The article is organised as follows:


1.0     Introduction

A military unit is a group having a prescribed size and a specific combat or support role within a larger military organisation. The chief military units in the ancient classical world were the phalanx of the Greeks and the legion of the Romans. The units used in modern armies have their origins in the 1500s to 1700s, when professional armies re-emerged in Europe after the end of the Middle Ages. The basic units of the company, battalion, regiment, brigade, division and corps have been retained since then.

Armies, navies, and air forces are organised hierarchically into progressively smaller units commanded by officers of progressively lower rank. The prototypical units are those of the army. The smallest unit in an army is the section or squad, which contains 7 to 14 soldiers and is led by a corporal or sergeant respectively. Three or four sections/squads make up a troop/platoon, which has 20 to 50 soldiers and is commanded by a 2nd lieutenant/lieutenant, assisted by a sergeant/staff sergeant.

Two or more troops/platoons make up a squadron/company, which has 100 to 250 soldiers and is commanded by a captain or a major, known as the officer commanding (OC). The OC, assisted by a warrant officer/sergeant major, is responsible for training, discipline and welfare of the company’s personnel. A company is the smallest body of troops that functions as a complete administrative and tactical unit. A company consists of a headquarters (usually administered by a sergeant and containing supply, maintenance, or other sections.) and two or more platoons organised and equipped to perform the company’s operational functions. It is usually commanded by a captain, who discharges the basic responsibilities for training, discipline, and providing for the welfare of the personnel. In medieval armies the term company referred loosely to the body of men accompanying a lord or knight into the field. As the organisation of European armies developed, individual companies were brought together in larger tactical formations and eventually became subunits of regiments and even subdivisions of brigades. Companies in modern armies vary widely in size and equipment, usually being established around a function or mission (e.g. signal repair, medical ambulance, engineer bridging, reconnaissance or military police companies) or around a weapon or class of weapons (e.g. tank, rifle or infantry or mortar companies). One characteristic all companies have in common, however, is basic administrative unity so that they can be absorbed as required into larger military formations, such as the battalion.

Two or more squadrons/companies make up a regiment/battalion, which is typically commanded by a lieutenant colonel, assisted by a warrant officer/senior sergeant major. The battalion is the smallest unit to have a staff of officers (in charge of personnel, operations, intelligence, and logistics etc.) to assist the commander. A regiment, in most armies, is a body of troops headed by a colonel and organised for tactical control into companies, battalions, or squadrons. French cavalry units were called regiments as early as 1558. The word is derived from the Latin regimen, a rule or system of order, and describes the regiment’s functions of raising, equipping, and training troops. As a regiment acquired individuality, colours, coat of arms, distinctive uniform and insignia, and achievements in battle, it also became a central object of loyalty, pride, and esprit de corps of its soldiers. A battalion is a tactical military organisation composed of a headquarters and two or more companies, batteries, or similar organisations and usually commanded by a field-grade officer. The term has been used in nearly every Western army for centuries and has had a variety of meanings. In the 1500 and 1600s, it denoted a unit of infantry forming part of a line of battle and was loosely applied to any large body of men. During the Napoleonic Wars, the French developed an army organisation in which the regiment was a unit of administration for its battalions serving as fighting units in the field. In this connection, the terms regiment and battalion often were used interchangeably, but in most modern armies the regiment is a higher unit than the battalion. In the armies of the Commonwealth nations, infantry battalions, usually commanded by lieutenant colonels, are tactical units formed within regiments, the latter being not tactical but administrative parent organisations. The equivalent tactical artillery and armoured units, however, are called regiments. In most military forces the cavalry equivalent and aviation equivalent of the battalion is the squadron.

Several battalions form a brigade, which is typically commanded by a brigadier general or a colonel. In the UK model combat troops are organised into battalions with regiments as administrative bodies, whereas combat service support troops (e.g. logistics) are organised into regiments (The term regiment can signify either a battalion or a brigade in different countries’ armies.) A brigade is the smallest unit to integrate different types of combat and support units into a functional organisation. A combat brigade, for example, usually has infantry, armour, artillery, and reconnaissance units.

Two or more brigades, along with various specialised regiments/battalions, make up a division and is usually commanded by a major general. A division contains all the arms and services needed for the independent conduct of military operations. Two to seven divisions and various support units make up an army corps, or a corps, which is typically commanded by a lieutenant general. The army corps is the largest regular army formation, though in wartime two or more corps may be combined to form a field army (commanded by a general), and field armies in turn may be combined to form an army group.

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