In military terminology, a battalion consists of two to six companies typically commanded by a lieutenant colonel. The nomenclature varies by nationality and by branch of arms, e.g. some armies organize their infantry into battalions, but call battalion-sized cavalry, reconnaissance, or tank units a squadron instead. There may even be subtle distinctions within a nation's branches of arms, such a distinction between a tank battalion and an armored squadron, depending on how the unit's operational role is perceived to fit into the army's historical organization.
A battalion is potentially the smallest military unit capable of independent operations (i.e. not attached to a higher command), but is usually part of a regiment or a brigade or both, depending on the organizational model used by that service. Battalions are ordinarily homogeneous with respect to type (e.g. an infantry battalion or a tank battalion), although there are occasional exceptions.
United States Army
An American battalion has between 300 to 1000 Soldiers or Marines, and consists of several companies. It is commanded by a lieutenant colonel, with majors serving as the executive officer and the Operations Officer (S-3).
Three to four battalions form a brigade.
In the 1960s to the present day, a typical infantry battalion has five companies: Headquarters and Headquarters Company (HHC), which includes the battalion staff; A, B, and C Companies, and a Combat Support Company, which includes scouts, anti-tank, and mortar sections or platoons.
American Army mechanized infantry battalions and tank battalions, for tactical purposes, will cross-post companies to each other, forming a battalion-sized task force (TF).
During the American Civil War a battalion was a tactical formation consisting of half the companies in a regiment.
The term battalion is used in the infantry, Royal Army Medical Corps and Royal Electrical and Mechanical Engineers only. It was formerly used in the Royal Engineers (occasionally) and the now defunct Royal Army Ordnance Corps and Royal Pioneer Corps. Other corps usually use the term regiment.
An infantry battalion usually has a Headquarters Company, Support Company and three Rifle Companies (usually, but not always, A, B and C). Each company is commanded by a major, the officer commanding (OC), with a captain as second-in-command. The HQ company contains signals, quartermaster, catering, intelligence, administration, pay, training, operations and medical elements. The support company usually contains anti-tank, machine gun, mortar, pioneer and reconnaissance platoons. Mechanised units will usually have an attached Light Aid Detachment (LAD) of the Royal Electrical and Mechanical Engineers (REME) to perform field repairs on vehicles and equipment.
Important figures in a battalion headquarters include: