Infantry, largest and oldest branch of all armies, made up of soldiers who fight chiefly on foot, using light weapons such as machine-guns, rifles, and grenades, and are equipped with antiarmour missiles, mortars, artillery, and armoured fighting vehicles. The infantry is charged with closing in to kill or capture the enemy, or repelling enemy assaults with fire and close combat. Infantry troops may move on foot, or by armoured vehicles, trucks, planes, or helicopters. Special units are trained for parachute and commando-type attacks. Mechanized infantry uses light armoured vehicles to provide the firepower and mobility to form an effective combined arms team with tank units. In the British Army an infantry regiment consists of battalions, further divided into companies. The United States Army has mechanized and light infantry divisions, divided into regiments. Foot soldiers traditionally fought in dense formations, such as the Greek phalanx. With the invention of firearms, they fought in long lines, eventually spreading out so as to make themselves harder to hit. Modern infantry units in the era of nuclear battlefield weapons are widely spread apart. The largest operating unit of infantry in the US Army, without increments from other branches, is the brigade, commanded by a colonel. The brigade regularly receives support from armour, artillery, engineer, signal, and logistical units.