and outside surveillance cameras allow protected observation from within the vehicle. Wheeled 4x4 and 6x6 configurations are typical of security vehicles. Tracked security vehicles are often cumbersome and leave negative political connotations for being perceived as an imperial invading force. Improvised fighting vehicle An improvised fighting vehicle is a combat vehicle resulting from modifications to a civilian or military non-combat vehicle in order to give it a fighting capability. Such modifications usually consist of the grafting of armour plating and weapon systems. Various militaries have procured such vehicles, ever since the introduction of the first automobiles into military service. During the early days, the absence of a doctrine for the military use of automobiles or of an industry dedicated to producing them, lead to much improvisation in the creation of early armoured cars, and other such vehicles. Later, despite the advent of arms industries in many countries, several armies still resorted to using ad hoc contraptions, often in response to unexpected military situations, or as a result of the development of new tactics for which no available vehicle was suitable. The construction of improvised fighting vehicles may also reflect a lack of means for the force that uses them. This is especially true in underdeveloped countries and even in developing countries, where various armies and guerrilla forces have used them, as they are more affordable than military-grade combat vehicles. Modern examples include military gun truck used by units of regular armies or other official government armed forces, based on a conventional military cargo truck, that is able to carry a large weight of weapons and armour. They have mainly been used by regular armies to escort military convoys in regions subject to ambush by guerrilla forces. "Narco tanks", used by Mexican drug cartels in the Mexican Drug War, are built from such trucks, which combines operational mobility, tactical offensive, and defensive capabilities. Troop carriers Troop-carrying AFVs are divided into three main types – armoured personnel carriers (APCs), infantry fighting vehicles (IFVs) and infantry mobility vehicles (IMV). The main difference between the three is their intended role – the APC is designed purely to transport troops and is armed for self-defence only – whereas the IFV is designed to provide close-quarters and anti-armour fire support to the infantry it carries. IMV is a wheeled armoured personnel carrier serving as a military patrol, reconnaissance or security vehicle. Armoured personnel carrier Armoured personnel