An armoured fighting vehicle (AFV) is an armed combat vehicle protected by armour, generally combining operational mobility with offensive and defensive capabilities. AFVs can be wheeled or tracked. Examples of AFVs are tanks, armoured cars, assault guns, self-propelled guns, infantry fighting vehicles (IFV), and armoured personnel carriers (APC). Armoured fighting vehicles are classified according to their characteristics and intended role on the battlefield. The classifications are not absolute; two countries may classify the same vehicle differently, and the criteria change over time. For example, relatively lightly armed armoured personnel carriers were largely superseded by infantry fighting vehicles with much heavier armament in a similar role. Successful designs are often adapted to a wide variety of applications. For example, the MOWAG Piranha, originally designed as an APC, has been adapted to fill numerous roles such as a mortar carrier, infantry fighting vehicle, and assault gun. Armoured fighting vehicles began to appear in use in World War I with the armoured car, the tank, the self-propelled gun, and the personnel carrier seeing use. By World War II, armies had large numbers of AFVs, together with other vehicles to carry troops this permitted highly mobile manoeuvre warfare. Evolution The concept of a highly mobile and protected fighting unit has been around for centuries; from Hannibal's war elephants to Leonardo's contraptions, military strategists endeavoured to maximize the mobility and survivability of their soldiers. Armoured fighting vehicles were not possible until internal combustion engines of sufficient power became available at the start of the 20th century. History Modern armoured fighting vehicles represent the realization of an ancient concept – that of providing troops with mobile protection and firepower. Armies have deployed war machines and cavalries with rudimentary armour in battle for millennia. Use of these animals and engineering designs sought to achieve a balance between the conflicting paradoxical needs of mobility, firepower and protection. Siege machine Siege engines, such as battering rams and siege towers, would often be armoured in order to protect their crews from enemy action. Polyidus of Thessaly developed a very large movable siege tower, the helepolis, as early as 340 BC, and Greek forces used such structures in the Siege of Rhodes (305 BC). The idea of a protected fighting vehicle has been known since antiquity. Frequently cited is Leonardo da Vinci's 15th-century sketch of a mobile, protected gun-platform; the drawings show a conical, wooden shelter with apertures for cannons around