See J. Keegan and R. Holmes, Soldiers (1980).
The Infantry is the oldest and most numerous of the Combat Arms in the armed forces, and consists of soldiers who predominantly fight on foot; an infantry soldier is an infantryman. Infantry units are the only types of land forces that can occupy and hold positions, and therefore have the most physically demanding training in the army, emphasizing physical fitness, physical strength, and aggressive character due to non-reliance on technology that augments marching all of which are required due to the primary role of the infantry to engage in ground combat.
Infantry can be distinguished from other types of soldiers: cavalry, tanks, technicians such as armourer and signaller. Nonetheless basic infantry skills are fundamental to the training of any soldier, and soldiers of any branch of an army are expected to serve as auxiliary infantry (i.e. patrol and fight on foot) when necessary.
Although the term infantry dates from the 15th century, the foot troops of the previous eras in history who fought with a variety of weapons before the introduction of the firearms are also referred to as infantry. During the Ancient and Middle Ages Infantry were categorized by the types of weapons and armour they used, such as heavy, medium, and light infantry. Since the introduction of firearms classifications have changed initially to reflect their formations on the battlefield as line infantry, and later to reflect modes of transport and type of tactics used by specific units as Mechanized infantry or airborne infantry.
Since the end of the Second World War infantry became a minority in armies of the Western world, constituting typically between 10% and 30% . This reflects the greatly increased requirement for technical and logistical specialists in Western armies, resulting from the increasing complexity of military technology and equipment and an increased recognition of the importance of logistics in warfare. In the Third world armies, infantry still accounts for a majority of the soldiers.
Infantry is arguably the most flexible of the Combat Arms, able to manoeuvre in terrain inaccessible to cavalry or armour, and employing infantry support weapons that can provide impromptu substitute for the artillery. However, the other Combat Arms are unable to operate without infantry support which ensures that any Combined Arms formation includes an infantry unit.
With the notable exception of the Mongol Empire, infantry has represented the largest component in most armies of the past, and the present. While the specific weapons have varied, the common factor is that these soldiers have relied on their feet for tactical movements, but since the introduction of the rail and motor transport have been operationally transported behind the front-lines, and have made use of strategic airlift with the introduction of aircraft into warfare. Of course infantry had always gone to anywhere the navies could take them around the globe.
During the Ancient history, infantry were essentially armed mobs, fighting in loosely organized opposing lines, under the vocal direction of individual commanders in the immediate vicinity of the troops' hearing range. However, the benefits of uniform equipment, weaponry and above all training led to the development of formations able to carry out pre-arranged tactical maneuvers in the heat of battle.
Since that time infantry organization has focused on finding a balance between heavily-armed formations that emphasise fire-power and ability to withstand direct assaults, and more lightly-armed but also more mobile units able to manoeuvre around the battlefield faster, to exploit tactical opportunities. Mobility, armament, and protection have been the three competing primary factors that complement and compete in the balanced approach to development of infantry doctrine throughout history.
Infantry was the primary combat arm of the Classical period. Examples of infantry units of the period are the hoplites of ancient Greece and the legions of Imperial Rome and Auxiliaries (Roman military) troops. In contrast to the strictly organized phalanxes and legions, most armies of the ancient world also employed units of irregulars (often mercenaries) who wore less armor and fought in more open formations usually as skirmishers.
As the Decline of the Roman Empire occurred across the huge swathe of lands under their sway to the depredations of Germanic tribes such as the Vandals, Goths, and Visigoths in the 5th century AD, the political and military resources necessary for the maintenance of such rigid-formation units largely disappeared until the later Middle Ages.
While bows remained in use long after the development of firearms, technological fine-tuning along with the development of the wheel-lock allowed firearms to supersede even the feared English longbow as the ranged weapon of choice for infantry during the early modern period. The bow also declined in favor due to the ease with which musketeers could be trained (days or weeks to attain moderate proficiency, as opposed to many years for the longbow).
After the Spanish Tercios, many other nations combined firearms with extremely long pikes into units that were virtually invincible against cavalry formations. Eventually, with the development of the bayonet, the pikemen were dropped from the formation, resulting in the first examples of an infantry unit as recognizable today.
In the 1890s and later, some countries, such as Italy with their Bersaglieri, used bicycle infantry, but the real revolution in mobility started in the 1920s with the use of motor vehicles, resulting in motorized infantry. Action in World War II demonstrated the importance of protecting the soldiers while they are moving around, resulting in the development of mechanized infantry, who use armored vehicles for transport. World War II also saw the first widespread use of paratroopers. These were soldiers that parachuted from airplanes into combat, and they played key roles in several campaigns in the European theater.
Most other present day infantry is either motorised or mechanised, supported by armored fighting vehicles, artillery, and aircraft, but along with light infantry which does not use armored fighting vehicles, is still the only kind of military force that can take and hold some terrain types (such as urban or other close terrain), and thus remains essential to fighting wars. However, the tactic of having massive formations of infantry on open terrain fight it out has fallen into disuse in Western armies ever since World War II. This is mainly because of advanced technology which can support, replace, and exceed the capabilities of infantry. Modern military doctrine supported by political influence have also kept the practice of total war and mass combat casualties to a minimum.
Infantry is notable by its reliance on organized formations to be employed in battle. These have been developed over time, but remain a key element to effective infantry development and deployment. Up until the 20th century, infantry units were for the most part employed in close organized formations up until the last moment possible. This was necessary to allow commanders to retain control of the unit, especially while maneuvering, as well as allowing officers to retain discipline amongst the ranks.
With the development of weapons with increased firepower, it became necessary to disperse the infantry over a wider expanse of terrain. This made the unit less susceptible to high explosive and rapid fire weapons. Modern infantry spacing on daytime patrols should be approximately 8m. From World War I, it was recognized that infantry were most successfully employed when using their ability to maneuver in constricted terrain and evade detection in ways not possible for other weapons such as vehicles. This decentralization of command was made possible by improved communications equipment and greater focus on small unit training.
Attack operations are the most basic role of the infantry, and along with defense, form the two primary stances of the infantry on the battlefield. Traditionally, in an open battle, or meeting engagement, two armies would maneuver to contact, at which point they would form up their infantry and other units opposite each other. Then one or both would advance and attempt to defeat the enemy force. The goal of an attack remains the same: to advance into an enemy-held objective and dislodge the enemy, thereby establishing control of the objective. Attacks are often feared by the infantry conducting them due to the high number of casualties suffered while advancing under enemy fire (mechanized infantry are considered in assaulting positions in contrast to light infantry due to armoured protection and high mobility). Successful attacks rely on sufficient force, preparative reconnaissance and bombardment, and retention of unit cohesion throughout the attack.
Defense operations are the natural counter to attacks, in which the mission is to hold an objective and defeat enemy forces attempting to dislodge the defender. Defensive posture offers many advantages to the infantry, including the ability to use terrain and constructed fortifications to advantage and the reduced exposure to enemy fire compared with advancing forces. Effective defense relies on minimizing losses to enemy fire, breaking the enemy's cohesion before their advance is completed, and preventing enemy penetration of defensive positions.
Patrol is the most common infantry mission. Full scale attacks and defensive efforts are occasional, but patrols are constant. Patrols consist of small groups of infantry moving about in areas of possible enemy activity to discern enemy deployments and ambush enemy patrols. Patrols are used not only on the front-lines, but in rear areas where enemy infiltration or insurgencies are possible.
Pursuit is a role that the infantry often assumes. The objective of pursuit operations is the destruction of enemy forces which are not capable of effectively engaging friendly units before they can build their strength to the point where they are effective. Infantry traditionally have been the main force to overrun these units in the past, and in modern combat are used to pursue enemy forces in constricted terrain (urban areas in particular), where faster forces, such as armored vehicles are incapable of going or would be exposed to ambush.
Escort consists of protecting other units from ambush, particularly from other infantry. This is one of the most important roles for the modern infantry, in particular when operating along side armored vehicles. In this capacity, infantry essentially conducts patrol on the move, scouring terrain which may hide enemy infantry waiting to ambush friendly vehicles, and identifying enemy strong points for attack by the heavier units.
Maneuver operations consume much of an infantry unit's time. Infantry, like all combat units, are often maneuvered to meet battlefield needs, and often must do so under enemy attack. The infantry must maintain their cohesion and readiness during the move to ensure their usefulness when they reach their objective. Traditionally, infantry have relied on their own legs for mobility, but mechanised or armoured infantry often uses trucks and armored vehicles for transport, leaving the light infantry to jobs which they cannot access.
Reserve assignments for infantry units involve deployment behind the front, although patrol and security operations are usually maintained in case of enemy infiltration. This is usually the best time for infantry units to integrate replacements into units and to maintain equipment. Additionally, soldiers can be rested and general readiness should improve. However, the unit must be ready for deployment at any point.
Construction can be undertaken either in reserve or on the front, but consists of using infantry troops as labor for construction of field positions, roads, bridges, airfields, and all other manner of structures. The infantry is often given this assignment due to the physical quantity of men within the unit, although it can lessen a unit's morale and limit the unit's ability to maintain readiness and perform other missions. More often, such jobs are given to specialist engineering corps.
'Base defense' is where infantry units are tasked to protect certain areas like command posts or airbases. Units assigned to this job usually have a large amount of military police attached to them for control of checkpoints and prisons.
Due to the very nature of the "work" with firearms, explosives, physical-emotional stress, and genuine violence, casualties and or deaths are not uncommon in both war and in peace. The infantryman is expected and trained to continue on with the mission despite personal fear, despair, fatigue and injury. These are exemplified in the United States Army by and excerpt from the infantryman's creed
In the race for victory, I am swift, determined, and courageous; Armed with a fierce will to win. Never will I fail my country's trust. Always I fight on: through the foe, to the objective, to triumph over all. If necessary, I fight to my death.
US Army Rangers, a specialised light infantry, have their own Ranger Creed that demands faithful service from the infantryman even "...though he be the lone survivor."
Life in an active duty infantry unit is rigorous, a 24 hour cycle makes for long hours of exercise/training/fighting/patrolling in often brutal climates armed only with the weapons, ammunition and essential war fighting equipment that they can carry on their backs. Remaining space is meant for a meal rations to fight their hunger. Infantry are usually afforded upwards of 4000 calories per day when on operations. Very little space is afforded for comforts. The physical demands are extreme. Forced marches, carrying in excess of 80lbs (36 kg) of equipment upwards of 25 miles (40 km) at a 4-6mi/h (6–10 km/h) pace is not uncommon. 15 mile runs at a forced pace are common as well. Mastering one's body is essential, as eating just one meal a day may be experienced occasionally when situations dictate such. Teamwork and absolute trust are essential for the survival of not only the individual, but the unit as a whole.
Very strong bonds that last an entire life time form within these infantry units and there is a sort of professional respect given from one infantryman to another, both inside and outside of the military, which is based on a common understanding of what life is like on the inside of an infantry battalion and the character and discipline of the individuals who comprise them.
The equipment of infantry forces has evolved along with the development of military technology in general, but certain constants remain regarding the design and selection of this equipment. Primary types of equipment are weaponry, protective gear, survival gear, and special equipment.
Infantry weapons have included all types of personal weapons, i.e. anything that can be handled by individual soldiers, as well as some small crew-served weapons that can be carried. During operations, especially in modern times, infantry often scavenge and employ whatever weapons they can acquire in addition to those given them by their supply chain.
Infantry from ancient times up until the modern age have wielded a wide array of weaponry. Infantry used all sorts of melee weapons, such as various types swords, axes, and maces, as well as ranged weapons such as javelins, bows, and slings. Infantry of these periods also often wore varying types of armor, including chain mail and Cuirasses. Many of their weapons evolved over time to counter advances made in armor, such as the falchion, whose heavy blade was designed to break chain mail armor.
Modern infantry weaponry include rifles, sub machine guns, machine guns, shoulder-fired rocket launchers and missiles, and lighter mortars and grenade launchers. Modern infantry are often equipped with helmets, a gas mask, and in some cases, additional body armor.
Infantry protective gear includes all equipment designed to protect the soldier against enemy attack. Most protective gear comprises body armor of some type. Classical and medieval infantry employed leather and metal armor as defense against both ranged and melee attacks, but with the advent of firearms, such armor could no longer defeat attacks and was discarded. The return to use of the helmet was prompted by the need to defend against high explosive fragmentation, and further developments in materials led to effective bullet-defeating armor within the weight acceptable for infantry use. The use of body armor is again becoming widespread amongst infantry units, primarily using Kevlar technology. Infantry must also often carry protective measures against chemical and biological attack, including gas masks, counter-agents, and protective suits.
Infantry survival gear includes all of the items soldiers require for day-to-day survival in the combat environment. These include basic environmental protections, medical supplies, food, and sundries. Traditionally, infantry have suffered large casualty rates from disease, exposure, and privation--often in excess of those suffered from enemy attacks. Better equipment of troops in this area greatly reduce this rate of loss. One of the most valuable pieces of gear is the entrenching tool--basically a small shovel--which can be employed not only to dig important defenses, but also in a variety of other daily tasks and even as an effective weapon.
Specialized equipment consists of a variety of gear which may or may not be carried depending on the mission and the level of equipment of an army. Communications gear has become a necessity, as it allows effective command of infantry units over greater distances. In some units, individual communications are being used to allow the greatest level of flexibility. Engineering equipment, including demolitions, mines, and other gear, is also commonly carried by the infantry or attached specialists. A variety of other gear, often relating to a specific mission, or to the particular terrain in which the unit is employed, can be carried by infantry units.