Armor (military branch)
Armor, when used to describe a branch of land combat forces, refers to those units that engage in combat using mobile and protected vehicles such as tanks, infantry fighting vehicles, and armored personnel carriers. Such units are often called heavy, which refers both to their strength and their logistical demands.
Armored warfare dervives from two seemingly opposed types of ancient military forces: cavalry and heavy (i.e., protected) infantry. The mounted and armored knight is an icon of combining speed, protection, and shock, but was actually a fairly rare force to find on actual battlefields.
Historical cavalry, mounted on horses, camels, or other appropriate animals, was the fastest-moving type of land force, although with logistical demands for animal fodder, replacement mounts, etc. Cavalry forces performed screening, reconnaissance, raids on isolated targets. In appropriate circumstances, cavalry could gallop, at high speed, into enemy forces, using the shock of their momentum and preferably traveling through the enemy to charge again, rather than engage in melee.
At the other end of the spectrum of mobility were literally armored infantry, slow-moving but with protective equipment that would resist many contemporary weapons.
The beginning of mechanized armored operation began with the early tanks of the First World War. Their role was to support foot infantry in the attack, by giving them protected fire support, the ability to cross or crush obstacles such as trenches and barbed wire, and, where possible, to let them advance with the tank as a shield.
By the Second World War, it was realized by some, but not all, nations that tanks could operate independently. They were most effective if accompanied by equally mobile infantry and artillery — or, in lieu of artillery, close air support by appropriate aircraft.
Again coming from mounted cavalry origins, helicopter-borne air assault units exceeded tank-heavy units in speed, which, at first, was their main defense. The first armed helicopters were very vulnerable to enemy fire, and relied on surprise and maneuver to survive.
Eventually, the attack helicopter developed, with both heavier protection and heavier weapons. Conceptually, attack helicopters can fight tanks by using longer-range antitank weapons, often moving evasively behind ground obstacles.