A regiment is a military unit, composed of a variable number of battalions – commanded by a Colonel. Depending on the nation, military branch, mission, and organization, a modern regiment resembles a brigade, in that both range in size from a few hundred to 5,000 soldiers (3 to 7 standard battalions). Generally, regiments and brigades are grouped as divisions. The modern regiment's size varies in number, scope, and administrative role from country to country (and might not exist in some military forces) and sometimes even within the military of the same nations.
The French term régiment entered military usage in Europe at the end of the 16th century, when armies evolved from collections of retinues who followed knights, to a formally organised, permanent military force. At that time, regiments usually were named after their commanding colonels, and disbanded at the end of the campaign or war. At that time, the colonel and his regiment might recruit from and serve several masters (countries). Later, it was customary to name the regiment by its geographic precedence in the line of battle, and to recruit from specific places, the cantons. The oldest, existent regiment is the Swedish Life Guards, although the French claim that their 1st Infantry Regiment is the eldest, being created in 1479 from the ancient "Bandes de Picardies".
In the 17th century brigades were formed as combined arms units (infantry, cavalry, artillery) that were more effective than the older, single-arms regiments; in many armies, brigades replaced regiments.
The regimental army organisation system often is contrasted to the "continental system" (adopted by European armies). In the continental system, the division is the functional army unit, and its commander the administrator of every aspect of the formation: his staff train and administer the soldiers, officers, and commanders of the division's subordinate units. Generally, divisions are garrisoned together and share the same installations, thus, in divisional administration, a battalion commanding officer is just another officer in a chain of command; soldiers and officers are transferred in and out of divisions as required.
In the regimental system, each regiment is responsible for recruiting, training, and administration; each regiment is permanently maintained, therefore, the regiment will develop its unique esprit de corps because of its unitary history, traditions, recruitment, and function. Usually, the regiment is responsible for recruiting and administrating a soldier's military career. Depending upon the country, regiments can be either combat units or administrative units or both.
Some regiments were designated geographic areas from which to recruit, and usually incorporated the place name to its regimental title. In other cases, regiments would recruit from a given age group within a nation (e.g. Zulu Impis), an ethnic group (e.g. the Gurkhas), or foreigners (e.g. the French Foreign Legion). In other cases, new regiments were raised for new functions within an army; e.g. the Fusiliers, the The Parachute Regiment (British Army), and the U.S. Army 75th Ranger Regiment.
The benefits of the regimental system are weighed against such drawbacks as hazardous regimental competition, a lack of interchangeability between units of different regiments, and more pronounced "old boy networks" within the military that may hamper efficiency and fairness.
Another key aspect of the regimental system is that the regiment or battalion is the key tactical building block. This flows historically from the colonial period, when battalions were widely dispersed and virtually autonomous, but is easily adapted to a number of different purposes. For example, a regiment might include different types of battalions (e.g. infantry or artillery) of different origins (e.g. regular or reserve).
Within the regimental system, soldiers, and usually officers, are always posted to a tactical unit of their own regiment whenever posted to field duty. In addition to combat units, other organizations are very much part of the regimental family: regimental training schools, serving members on "extra-regimental employment", regimental associations (retirees), bands and associated cadet groups. The aspects that an administrative regiment might have in common include a symbolic colonel-in-chief (often a member of the royal family), a colonel of the regiment or "honorary colonel" who protects the traditions and interests of the regimental family and insists on the maintenance of high standards, battle honours (honours earned by one unit of an administrative regiment are shared by the whole regiment), ceremonial uniforms, cap badges, peculiarities of insignia, stable belts, and regimental marches and songs. The regiment usually has a traditional "home station", which is often a historic garrison that houses the regimental museum and regimental headquarters. The latter has a modest staff to support regimental committees and administer both the regular members and the association(s) of retired members.
In the British Army and armies modelled on it (such as the Australian, the Canadian, the Indian and the Pakistani), the term regiment is used confusingly in two different ways: it can mean an administrative identity and grouping or a tactical unit. The modern British regimental system came about as a result of the 19th century Cardwell Reforms.
In the United Kingdom, until recently there existed a number of administrative "divisions" in the infantry that encompassed several regiments, such as the Guards Division, the former Scottish Division (now a single regiment), or the Light Division (now also compressed into a multi-battalion single regiment). The down-sizing and consolidation of British infantry regiments that began in the late 1950s and concluded in 2006 has resulted in a system of administrative regiments each with several battalions, a band, a common badge and uniform etc.
In other Commonwealth countries such as India, Pakistan, Australia, New Zealand and Canada the large administrative regiment has been the normal practice for many years. In the case of India "large regiments" of four to five battalions date from 1923 and since the 1950s many of these have expanded even further. As an example the Punjab Regiment has expanded from four battalions in 1956 to its present strength of 20, while in Pakistan several regiments have over 50 battalions. More typically of Commonwealth armies with smaller establishments, in Australia there is but one administrative infantry regiment, the Royal Australian Regiment, consisting of all eight regular infantry battalions in the Army, including mechanised, motorised, light and para infantry.
In Pakistan the word regiment is an administrative grouping. While different battalions may have different roles (for example different battalions of the Frontier Force Regiment may be mechanized infantry, para infantry or mountain troops) the regiment is considered to encompass all of them.
In the British Army, for most purposes, the regiment is the largest "permanent" organisational unit. Above regimental level, organisation is changed to meet the tasks at hand. Because of their permanent nature, many regiments have long histories, often going back for centuries; the oldest British regiment still in existence is the Honourable Artillery Company, established in 1537. The Royal Scots, formed in 1633, was the oldest infantry regiment. It now forms part of the Royal Regiment of Scotland.
In the British regimental system the tactical regiment or battalion is the basic functional unit and its Commanding Officer more autonomous than in a continental system. Divisional and brigade commanders generally do not immerse themselves in the day-to-day functioning of a battalion – they can replace the commanding officer but will not micro-manage the unit. The regimental sergeant major is another key figure, responsible to the CO for unit discipline and the behaviour of the NCOs.
In those armies where the system exists, the regimental system is criticized as parochial and as creating unnecessary rivalry between different regiments. The question is also raised as to whether it is healthy to develop soldiers more loyal to their regiment than to the military in general. It is worth noting that the United Kingdom, for example, has never suffered a military coup, or even seriously faced the prospect of one – this could be attributed to the "tribal" nature of the regimental system, which makes it nearly impossible for a charismatic leader to command the loyalty of the entire army. Commonwealth-style regiments have proven their worth throughout history in war and through lengthy and difficult policing missions. Regiments recruited from areas of political ferment (such as Scotland, Wales, Ireland, Quebec, India, etc.), tend to perform particularly well because of the loyalty their members exhibit to the regiments. Generally, the regimental system is found to best function in countries with small- to medium-sized military forces where the problems of administering vast numbers of personnel are not as prevalent. The regimental system works particularly well in an environment where the prime role of the army is small-scale police actions and counterinsurgency operations, requiring prolonged deployment away from home. In such a situation, co-ordination between regiments is rarely necessary, and the esprit de corps of the regiment provides an emotional substitute for the sense of public approval that an army receives at home. This is particularly relevant to British experience during the days of the empire, where the army was virtually continuously engaged in low-intensity conflict with insurgents, and full-scale warfare was the exception rather than the rule.
Further, the regimental system offers the advantage of grouping like units together for administrative, training, and logistical purposes, thereby creating an “economies of scale” effect and its ensuing increased efficiency. An illustrative example is the USMC that can take elements from its regimentally grouped forces and specifically tailor combined arms task forces for specific missions or its deployed MEUs. This is achievable partially because of the Marines mission flexibility philosophy, shared culture, history, and overall esprit de corps, which allows for near seamless modular integration.
It should however be noted that a series of amalgamations beginning in the late 1950s and ending in 2006 have diluted the British regimental system through the now almost universal adoption of "large regiments" for the infantry and cavalry branches of the Army. These units comprise up to six of the former battalions that previously had separate regimental status. Only the Guards regiments retain their historic separate identities.
Irish Army field artillery units are called regiments. They are divided into batteries and together form the Artillery Corps. At present there are two artillery regiments per brigade, one full-time regular regiment and one part-time reserve regiment. Irish Army Air Defence units are called batteries and collectively form a regiment. Batteries are dispersed throughout the country and encompass both regular and reserve formations.
In practice, it is impossible to exercise all the administrative functions of a true regiment when the regiment consists of a single unit. Soldiers, and particularly officers, cannot spend a full career in one battalion. Thus in the Armoured Corps, the traditional administrative "regiment" tends to play more of a ceremonial role, while in practise, its members are administered by their corps or "branch" as in the Artillery. Thus soldiers and officers can serve in many different "regiments", changing hat badges without too much concern during their career. Indeed, in the artillery, all regiments wear the same badge.
Historically, a regiment consisted of 3 battalions and the regiment headquarters (Hq) company.
A new system, the Combat Arms Regimental System, or CARS, was adopted in 1957 to replace the old regimental system. CARS uses the Army's traditional regiments as parent organizations for historical purposes, but the primary building blocks of divisions and brigades became battalions. Each battalion carries an association with a parent regiment, even though the regimental organization no longer exists. In some brigades several numbered battalions carrying the same regimental association may still serve together, and tend to treat themselves as part of the traditional regiment when in fact they are independent battalions serving a brigade headquarters and not a regimental one. The CARS was substituted by United States Army Regimental System (USARS) in 1981.
There are, of course, exceptions to USARS, including the Armored Cavalry Regiments, The Old Guard, which is the Army's ceremonial unit at Fort Myer, VA that retained its historical title of the 3rd U.S. Infantry Regiment, and the 75th Ranger Regiment that was created in 1986. Training, administration and even tactical employment was centred at divisional level. Many, but not all combat support and logistics was also concentrated at that level.
The United States Marine Corps deploys battalions from its regiments in Marine Expeditionary Units or MEU's. However, a USMC regiment may deploy en masse as the ground combat element of a Marine Expeditionary Brigade or MEB. When attached to the MEB the Regiment is reinforced and redesignated a Regimental Landing Team.
The regiments (полк) of the Russian Army, and armed forces influenced by Russia consist of battalions (батальон), in the infantry or tank troops, divizions (дивизион) in the artillery troops, and squadrons (эскадрилья) in aviation troops. Land forces regiments also include support units – companies (рота) and/or platoons (взвод).