Infantry is an army specialization whose personnel engage in military combat on foot, distinguished from cavalry, artillery and armored forces. Also known as foot soldiers or infantrymen, infantry combatants traditionally also relies on traveling by foot between combats as well, but may still use mounts (mounted infantry), military vehicles (motorized and mechanized infantry) or other form of transport such as watercraft (naval infantry) or aircraft (airborne infantry) for non-combat mobility and logistics. Infantry make up a large portion of all armed forces in most nations, and typically bear the largest brunt in warfare, as measured by casualties, deprivation, or physical and psychological stress.
The first military forces in history were infantry. In antiquity, infantry were armed with early melee weapons such as a spear, axe or sword, or an early ranged weapon like a javelin, sling or bow, with a few infantrymen having both a melee and a ranged weapon. With the development of gunpowder, infantry began converting to primarily firearms. By the time of Napoleonic warfare, infantry, cavalry and artillery formed a basic triad of ground forces, though infantry usually remained the most numerous. With armoured warfare, armoured fighting vehicles have replaced the horses of cavalry, and airpower has added a new dimension to ground combat, but infantry remains pivotal to all modern combined arms operations.
Infantry have much greater local situational awareness than other military forces, due to their inherent intimate contact with the battlefield ("boots on the ground"); this is vital for engaging and infiltrating enemy positions, holding and defending ground (any military objectives), securing battlefield victories, maintaining military area control and security both at and behind the front lines, for capturing ordnance or materiel, taking prisoners, and military occupation. Infantry can more easily recognise, adapt and respond to local conditions, weather, and changing enemy weapons or tactics. They can operate in a wide range of terrain inaccessible to military vehicles, and can operate with a lower logistical burden. Infantry are the most easily delivered forces to ground combat areas, by simple and reliable marching, or by trucks, sea or air transport; they can also be inserted directly into combat by amphibious landing, or for air assault by parachute (airborne infantry) or helicopter (airmobile infantry). They can be augmented with a variety of crew-served weapons, armoured personnel carriers, and infantry fighting vehicles.