Armoured Vehicle Research

An armoured fighting vehicle is a combat vehicle, protected by strong armour and armed with weapons. AFVs can be wheeled or tracked.
Armoured fighting vehicles are classified according to their intended role on the battlefield and characteristics. This classification is not absolute; at different times different countries will classify the same vehicle in different roles. For example, armoured personnel carriers were generally replaced by infantry fighting vehicles in a very similar role, but the latter has some capabilities lacking in the former.

History

The first AFVs were armoured cars, dating back virtually to the invention of the motor car. Such vehicles were largely used as scouting vehicles, and were armoured to protect the crew. The development of the AFV continued into World War I, when the tracked tank was introduced on the Western Front a machine that was armoured because it was specifically designed to be fired upon.

The tank proved highly successful, and as technology improved the tank became a weapon that could cross large distances at much higher speeds than supporting infantry and artillery. The need to provide the units that would fight alongside the tank led to the development of the wide range of AFVs that exist today, with most armies having vehicles to carry infantry, artillery and anti-aircraft weaponry by the end of World War II. Most modern AFVs are superficially similar in design to their World War II counterparts, with significantly better armour, weapons, engines and suspension - however with an increase in the capacity of transport aircraft allowing AFVs to be practically transported by air, many armies are replacing some or all of their traditional heavy vehicles with lighter airmobile versions, often with wheels instead of tracks.
http://en.wikipedia.org/wiki/Armoured_fighting_vehicle

Tank

The tank is an all terrain AFV designed primarily to engage enemy forces by the use of direct fire in the frontal assault role. Though several configurations have been tried, particularly in the early experimental days of tank development, a standard, mature design configuration has since emerged to a generally accepted pattern. This features a main artillery gun, mounted in a fully rotating turret atop a tracked automotive hull, with various additional machine guns throughout.
Philosophically, the tank is, by its very nature, an offensive weapon. Being a protective encasement with at least one gun position, it is essentially a pillbox or small fortress that can move toward the enemy hence its offensive utility.

Historically, tanks are divided into 3 categories: Light Tanks, small, thinly armoured, weakly gunned, but highly mobile tanks intended for the armoured reconnaissance role, Medium Tanks, mid-sized, adequately armoured, respectably gunned, fairly mobile tanks intended to provide an optimum balance of characteristics for manoeuvre combat, primarily against other tanks and Heavy Tanks large, thickly armoured, powerfully gunned, but barely mobile tanks intended for the breakthrough role against fortified lines, particularly in support of infantry formations.
http://en.wikipedia.org/wiki/Armoured_fighting_vehicle

Armoured personnel carrier

Armoured personnel carriers are intended to carry infantry quickly and relatively safely to point where they are deployed. In 1918, the British Mk V tank was capable of carrying a small number of troops and in 1944, the Canadian general Guy Simonds ordered the conversion of redundant armoured vehicles to carry troops. This proved highly successful, even without training, and the concept was widely used in the 21st Army Group. Post-war, specialised designs were built, culminating in the Soviet BTR-60 and US M113
http://en.wikipedia.org/wiki/Armoured_fighting_vehicle

Infantry fighting vehicle

An infantry fighting vehicle is an armoured personnel carrier which can provide significant fire support. The first IFV was the Soviet BMP-1, which surprised western intelligence analysts when it appeared in a military parade in 1967.

Modern IFVs are well-armed infantry carriers, differencing from earlier APCs by their heavier armament allowing them to give direct-fire support during an assault. Many also have firing ports allowing the infantry to fire personal weapons while mounted and improved armour. They are typically armed with a twenty millimetre or larger autocannon, and possibly with ATGMs. IFVs are usually tracked, but some wheeled vehicles fall into this category, too.
Specially-equipped IFVs have taken on some of the roles of light tanks; they are used by reconnaissance organizations, and light IFVs are used by airborne units which must be able to fight without the heavy firepower of tanks.
http://en.wikipedia.org/wiki/Armoured_fighting_vehicle