Infantry is the branch of an army trained to fight on foot — soldiers specifically trained to engage, fight, and defeat the enemy in face-to-face combat. Infantrymen thus bear the brunt of warfare, and suffer the greatest number of casualties. Historically, as the oldest branch of the combat arms, the infantry are the backbone of a modern army, and continually undergo training that is more physically stressful and demanding than that of any other branch of the combat arms, or of the army. The infantry’s greater emphasis upon discipline, physical fitness, and psychological strength develops reflexive skills that enable spontaneous, sustained aggression and violence, which make a weapon-system of the infantryman, whether armed or unarmed.
20th-century infantry: The Royal Irish Rifles at the Battle of the Somme (July–November 1916) during the First World War (1914–18).
Infantrymen are distinguished from soldiers trained to fight on horseback (cavalry), from tanks (armoured cavalry), with heavier long-range weapons (artillery), and as technicians (armourer, signaller, medic), by their greatly developed combat skills, such as movement techniques (by the individual, squad and platoon), firearms proficiency (individual and crew-served), and field craft. Infantry can enter and manœver in terrain that is inaccessible to military vehicles and tanks, and employ crew-served infantry support weapons that provide greater and more sustained firepower, in the absence of artillery. The transport and delivery techniques of infantrymen to engage in battle include marching, mechanised transport, airborne (by parachute), air assault (by helicopter), and amphibious.