Light infantry

Traditionally light infantry (or skirmishers) were soldiers whose job was to provide a skirmishing screen ahead of the main body of infantry, harassing and delaying the enemy advance. Light infantry was distinct from medium, heavy or line infantry. Heavy infantry were dedicated primarily to fighting in tight formations that were the core of large battles. Light infantry often fought in close co-ordination with heavy infantry, where they could screen the heavy infantry from harassing fire, and the heavy infantry could intervene to protect the light infantry from attacks of enemy heavy infantry or cavalry. Heavy infantry originally had heavier arms and more armour than light infantry, but this distinction was lost as the use of armour declined and gunpowder weapons became standardized.

Antiquity
The concept of a skirmishing screen is a very old one and was already well-established in Ancient Greece and Roman times in the form, for example, of the Greek peltast and the Roman velites. As with so called 'light infantry' of later periods, the term more adequately describes the role of such infantry rather than the actual weight of their equipment. Peltast equipment, for example, grew steadily heavier at the same time as hoplite equipment grew lighter. It was the fact that peltasts fought in open order as skirmishers that made them light infantry and that hoplites fought in the battle line in a phalanx formation that made them heavy infantry.

Modern age
Early regular armies of the modern era frequently relied on irregulars to perform the duties of light infantry skirmishers. In the 17th century, dragoons were the light infantry skirmishers of their day – lightly armed mounted infantrymen who rode into battle but dismounted to fight, giving them a mobility lacking to regular foot soldiers.

In the 18th and 19th centuries most infantry regiments or battalions had a light company as an integral part of its composition. Its members were often smaller, more agile men with high shooting ability and capability of using initiative. They did not usually fight in disciplined ranks as did the ordinary infantry but often in widely dispersed groups, necessitating an understanding of skirmish warfare. They were expected to avoid melee engagements unless necessary, and would fight ahead of the main line to harass the enemy before falling back to the main position.

During the period 1777-1781, the Continental Army of the United States adopted the British Army practice of seasonally drafting light infantry regiments as temporary units during active field operations, by combining existing light infantry companies detached from their parent regiments.

Light infantry sometimes carried lighter muskets than ordinary infantrymen while others carried rifles and wore rifle green uniforms. These became designated as rifle regiments in Britain and Jäger (hunter) regiments in German speaking Europe. In France, during the Napoleonic Wars, light infantry were called voltigeurs and chasseurs and the sharpshooters tirailleurs. The Austrian army had Grenzer regiments from the middle of the 18th century, who originally served as irregular militia skirmishers recruited from mountainous frontier areas. They were gradually absorbed into the line infantry becoming a hybrid type that proved successful against the French, to the extent that Napoleon recruited several units of Austrian army Grenzer to his own army after victory over Austria in 1809 compelled the Austrians to cede territories from which they were traditionally recruited. In Portugal, 1797, companies of Caçadores (Hunters) were created in the Portuguese Army, and in 1808 lead to the formation of independent "Caçador" battalions that became known for their ability to perform precision shooting at long distances.

Light infantry officers sometimes carried muskets or rifles, rather than pistols, and their swords were light curved sabres; as opposed to the heavy, straighter swords of other infantry officers. Orders were sent by bugle or whistle instead of drum (since the sound of a bugle carries further and it is difficult to move fast when carrying a drum). Some armies, including the British and French, recruited whole regiments (or converted existing ones) of light infantry. These were considered elite units, since they required specialised training with emphasis on self-discipline, manoeuvre and initiative to carry out the roles of light infantry as well as those of ordinary infantry.

By the late 19th century the concept of fighting in formation was on the wane due to advancements in weaponry and the distinctions between light and heavy infantry began to disappear. Essentially, all infantry became light infantry in operational practice. Some regiments retained the name and customs, but there was in effect little difference between them and other infantry regiments.

Not exactly the Light Role but very similar was infantry regiments of the Paraguayan Army during the Chaco War, who in small groups outed the larger and better equipped Bolivian Army in the Battle of Boqueron. The Paraguayan Army, much like the British rifle regiments wore a dark green uniform with bush hats.

Contemporary light infantry forces
Today the term "light" denotes, in the United States table of organization and equipment, units lacking heavy weapons and armor or with a reduced vehicle footprint. Light infantry units lack the greater firepower, tactical mobility and core defense possessed of heavy units, but possess greater operational mobility and the ability to execute missions under restrictive terrain and weather that would impair a heavy unit's mobility. Light infantry forces typically rely on their ability to operate under restrictive conditions, surprise, violence of action, training, stealth, field craft, and fitness level of the individual soldier to address their reduced lethality. Ironically, forces in a light unit will normally carry heavier individual loads versus other forces; they must carry everything they require to fight, survive and win due to lack of vehicles. Although units like the 101st Airborne (Air Assault) and the 82nd Airborne Division are categorized as Air Assault Infantry and Airborne Infantry respectively, they fall under the overall concept of light infantry.

In the 1980s, the United States Army increased light forces to address contingencies and increased threats requiring a more deployable force able to operate in restrictive environments for limited periods. At its height, this included the 6th Infantry Division (light), 7th Infantry Division (light), 10th Mountain Division (light infantry), 25th Infantry Division, and the 75th Ranger Regiment. Operation Just Cause is often cited as proof of concept. Almost 30,000 U.S. Forces, mostly light, deployed to Panama within a 48 hour period to execute combat operations.

During the 1990s, the concept of purely light forces came under scrutiny due to their decreased lethality and survivability. This scrutiny has resulted in the Stryker Brigade Combat Team, a greater focus on task organized units (such as Marine Expeditionary Units) and a reduction of purely light forces.

Despite their reduction, light forces have proven successful in Afghanistan (Operation Enduring Freedom), underlining the continued need for light infantry.

Modern Light Infantry Units

 * Infantry intended for difficult terrain such as mountains (United States Army 10th Mountain Division, United States Army 86th Infantry Brigade Combat Team (Mountain), Italian Army Alpini, French Army 27ème bataillon de Chasseurs alpins) or jungle (Philippine Army Scout Rangers, Brazilian Army Jungle Infantry Brigades).
 * Canada - Princess Patricia's Canadian Light Infantry 3rd Battalion capable in airborne, mountain, and amphibious operations.
 * India - Jammu and Kashmir Light Infantry, Sikh Light Infantry, and the Maratha Light Infantry regiments form part of the infantry Orbat.
 * United States Army 75th Ranger Regiment: a flexible, highly trained, and rapidly deployable airborne light infantry unit, used for special operations.
 * Seaborne or ship-based units, such as the United States Marine Corps' MEU (SOC) and Britain's 3 Commando Brigade.
 * Internal security or paramilitary troops and police field forces.
 * Troops involved in guerrilla or counter-guerrilla warfare.
 * Home defense or militia.