military unit, a group having a prescribed size and a specific combat or support role within a largermilitary organization. The chief military units in the ancient classical world were thephalanx of theGreeks and thelegion of theRomans. The units used in modern armies have their origins in the 16th–18th century, when professional armies reemerged inEurope after the end of theMiddle Ages. The basic units of thecompany,battalion,brigade, anddivision have been retained since then.

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Armies,navies, andair forces are organized hierarchically into progressively smaller units commanded by officers of progressively lower rank. The prototypical units are those of the army. The smallest unit in anarmy is thesquad, which contains 7 to 14 soldiers and is led by asergeant. (A slightly larger unit is asection, which consists of 10 to 40 soldiers but is usually used only within headquarters or support organizations.) Three or foursquads make up aplatoon, which has 20 to 50 soldiers and is commanded by alieutenant. Two or more platoons make up acompany, which has 100 to 250 soldiers and is commanded by acaptain or amajor. The function of administration is introduced at this level, in the form of aheadquarters platoon administered by a sergeant and containing supply, maintenance, or other sections.

Two or more companies make up abattalion, which has 400 to 1,200 troops and is commanded by alieutenant colonel. The battalion is the smallest unit to have astaff of officers (in charge of personnel, operations, intelligence, and logistics) to assist the commander. Several battalions form abrigade, which has 2,000 to 8,000 troops and is commanded by abrigadier general or acolonel. (The termregiment can signify either a battalion or a brigade in different countries’ armies.) A brigade is the smallest unit tointegrate different types ofcombat andsupport units into a functional organization. Acombat brigade, for example, usually hasinfantry, armour,artillery, and reconnaissance units.

Two or more brigades, along with various specialized battalions, make up adivision, which has 7,000 to 22,000 troops and is commanded by amajor 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 anarmy corps, or a corps, which has 50,000 to 300,000 troops and is commanded by alieutenant general. The armycorps is the largest regular army formation, though in wartime two or more corps may be combined to form afield army (commanded by ageneral), and field armies in turn may be combined to form an army group.

Naval units follow somewhat more-flexible organizational guidelines. Administratively, several ships of the same type (e.g.,destroyers) are organized into asquadron. Several squadrons in turn form aflotilla, several of which in turn form afleet. For operations, however, many navies organize their vessels intotask units (3–5 ships), task or battle groups (4–10 ships),task forces (2–5 task groups), and fleets (several task forces).

The basic fighting unit in anair force is the squadron, which consists of several aircraft of the same type—e.g.,fighters, and often of the same model—e.g.,F-16s. Three to six flying squadrons and their support squadrons make up awing. (An intermediate unit between the squadron and the wing is theair group or group, which consists of two to four squadrons.) Several wings are sometimescombined to form anair division or an air force.