From its humble beginnings during the Battle of the Somme in 1916, the tank has emerged as the most representative weapon of land warfare due to its combination of firepower, protection, and speed. However, mechanized armies require a plethora of different combat vehicles to provide mobility and fire support for the infantry, reconnaissance, and other secondary roles. Artillery has also become mechanized given the obvious advantages of mobility compared to their simpler, towed counterparts.
Heavy Tank: The original Mark I tanks that were introduced by the British Army in 1916 were lumbering behemoths that were truly the first heavy tanks in existence: tanks that maximized their firepower and protection at the expense of speed. This philosophy was taken to their maximum expression by the Wehrmacht and Red Army during World War II which fielded superb heavy tanks like the Tiger and Panther as well as the KV and IS series (USSR). These typically had gun calibers of over 76-mm and weighed over 40 tons. The British 'infantry tank' concept (exemplified by the Churchill) was similar to the heavy tank, albeit with lighter armament designed for infantry support rather than tank-to-tank combat. The advent of more powerful engines eventually negated the speed restrictions of heavy tanks which became largely obsolete in the 1950s once Main Battle Tanks became the standard.
Light Tank: The Renault FT-17 (France) entered service in 1918 and revolutionized tank design thanks to its speed and turreted gun. Although tanks would gradually get bigger during the interwar years, even at the start of World War II most armored forces were composed primarily of light tanks like the Panzer I and II (Germany). However, the quick rise in gun calibers and armor thickness following the early Blitzkrieg campaigns left light tanks increasingly relegated to reconnaissance or other secondary duties although some countries like Italy and Japan continued to rely heavily on them throughout the conflict. A small number of light tank designs were produced during the Cold War, mostly for specialized duties like airborne operations like the M551 Sheridan (US) or amphibious assaults like the PT-76 (USSR).
Medium Tank: The medium tank emerged as the standard tank type during World War II, having an ideal mix of firepower, armor thickness, and speed. A typical World War II-era medium tank weighed around 25-30 tons and had a gun caliber of at least 50-mm, although 75/76-mm was more common by 1943-45. The two most widely produced tanks of World War II were medium tanks, these being the T-34 (USSR) and the M4 Sherman (US), the latter which became the standard tank of both the US and British armies for their liberation of Western Europe. The British 'cruiser tank' concept (exemplified by the Crusader and Cromwell) was also similar. By the end of the war, the goal of maximizing firepower and protection without sacrificing speed became technologically feasible thus rendering the medium tank obsolete.
Main Battle Tank: The main battle tank (MBT) has been standard tank design since the end of World War II, rendering the older medium/heavy distinctions largely irrelevant given that they combine the best attributes of both. MBTs have gone through three major generations which have incorporated design philosophies based on the technologies of their eras. Additionally, some consider some of the newest MBTs part of a fourth generation. They are described as follows:
Tank Destroyer (TD): A tank destroyer is a vehicle designed to be a tank hunter while lacking some of the characteristics of a tank in order to reduce cost. These have followed different design philosophies depending on the army employing them. Early World War II tank destroyers were essentially anti-tank guns mounted on the chassis of a light tank such as in the Panzerjäger and Marder series (Germany). Late war tank destroyers, however, were much larger and heavily armored as well as was the case with the Elephant and Jagdpanther (Germany) which had some of the thickest armor of any wartime fighting vehicle but which were simpler to produce than a tank due to their lack of turrets; their guns were installed on the chasis superstructure. Others like the SU-85/100 (USSR) sat somewhere in the middle. US tank destroyers like the M10 Wolverine and M36 Jackson followed a different philosophy than their German and Soviet counterparts, packing the same gun as found on its M4 and M26 tanks (or a 17-pdr gun in British service) in a turret, but lightly armored in order to maximize speed. Most post-war tank destroyers have been based around ATGMs, usually mounted on an existing APC chassis. However, some gun platforms have appeared in recent years, notably the B1 Centauro (Italy) and the M1128 mobile gun system version of the Stryker (US).
Assault Gun (AG): The assault gun is superficially similar to the tank destroyer (at least their German and Soviet interpretations) but serves a different purpose, namely that of infantry support. As such they usually have higher caliber guns than tank destroyers but optimized for high-explosive rather than armor-piercing rounds. In contrast to the relative sizes of their tank destroyers, German assault guns were typically smaller and less heavily protected as was the case with the StuG III, the most widely produced German armored fighting vehicle of the war and which was roughly the size and weight of a medium tank (it was based on the Panzer III chassis) but considerably cheaper. In contrast, Soviet assault guns were veritable monsters, incorporating 122-mm or even 152-mm guns in the ISU-122 and ISU-152 respectively. Despite their intended role as infantry support, guns of these calibers could destroy most tanks as well and so these vehicles are often interchangeably referred to as tank destroyers. Many have also been referred to as self-propelled guns although a key distinction is that an assault gun is intended for direct rather than indirect fire. Neither the US nor British armies developed purposely-built assault guns although some medium tanks were modified with infantry support guns such as the M4(105). The assault gun concept largely disappeared in the post-war period, aside from a few designs focused on airborne use like the M56 Scorpion (US) and ASU-85 (USSR).
Armored Personnel Carrier (APC): Armored personnel carriers (APCs) were introduced in World War II as a means to transport a squad of infantry throughout the battlefield and enable them to keep up with armored units. Widespread use of APCs enabled the US and British armies to be the first fully motorized armies, in contrast to the more limited use of them in Panzer and Panzergrenadier units of the German army. APCs came in different flavors such as the fully tracked Universal Carrier (UK) or the M3 (US) and SdKfz 251 (Germany) half-tracks, and most have some limited combat capability (usually a roof-mounted machine gun) and some degree of protection against small-caliber ammunition though they are not meant for combat. Most major armies fully motorized in the 1950s and the Cold War gave some notable designs such as the US M113, the most widely built tracked APC ever built, as well as the Soviet BTR series, whose unique chassis design became the basis of nearly every wheeled APC since like the Piranha (Switzerland), LAV III (Canada) and Stryker (US). There has been a trend in the post-Cold War period towards wheeled rather than tracked APCs given their lower cost, easier maintenance, and superior road performance (albeit at the cost of inferior off-road performance). This has also resulted in a proliferation of APC designs with over two dozen countries currently producing them (and aggressively marketing them for export). APCs are also increasingly adopting a modular design, such as the German/Dutch Boxer which comes with various armor configurations and can also be converted into different roles.
Infantry Fighting Vehicle (IFV): IFVs are similar to APCs in that they are meant to transport a squad of infantry across the battlefield. Unlike APCs, IFVs are fully combat capable and are typically equipped with a rapid-firing autocannon of at least 20-mm caliber and often, anti-tank guided missiles (ATGMs) as well. Firing ports are also provided to the troop compartment so that the infantry can fire from inside the vehicle. Pioneered by the Bundeswehr, the USSR was the first of the two Cold War superpowers to adopt IFVs on a mass basis with their BMP series which entered service in the late 1960s, though these were quickly followed by NATO designs such as the Marder (Germany), M2/M3 Bradley (US), and Warrior (UK). Most IFVs are tracked in order for them to have the same cross-country capabilities of tanks, but they are also found in wheeled versions such as the French VCMI. Infantry forces that are based around IFVs rather than APCs are considered mechanized rather than motorized.
Infantry Mobility Vehicle (IMV): This is a relatively new classification used on light APCs that are the modern equivalent to a scout car, serving as personnel carriers, reconnaissance, or security vehicles. Physically, they resemble militarized versions of civilian off-road vehicles, confering protection against small-caliber rounds and usually providing some firepower of their own in the form of a roof-mounted machine gun. IMVs are usually cheap and unsophisticated enough that they can be produced even by smaller armies. Examples include the Bushmaster (Austrialia), Dingo (Germany), as well as the MRAP program of mine-resistant vehicles used extensively by the US and Coalition forces in Iraq and Afghanistan.
Armored Car (AC): The armored car was the first use of the motor vehicle in a combat role, providing a fast-moving platform for machine guns or other small-caliber weapons while offering some degree of protection for their crews. Their introduction predated World War I and by World War II were used primarily for armed reconnaissance. Armored cars were designed in various wheeled configurations and typically carried armament similar to that of light tanks although this varied considerably. For example, the Humber (UK) and M8 (US) had 37-40-mm guns whereas the Sd.KFz. 234/2 (Germany) weighed 10 tons and carried a 75-mm gun, making it heavier and more powerful than a Panzer I or II. After the war, armored cars remained attractive for countries looking for fast, powerfully-armed vehicles but which could not afford more expensive. Examples of these include the Panhard ABL (France), Saladin (UK), and the EE-9 Cascavel (Brazil), the first of which was one of the most widely used combat vehicles of the Cold War.
Scout Car (SC): Nearly identical to the armored car but less powerfully armed (typically only machine guns) or in some cases are unarmed altogether. They are used primarily for scouting and observation duties where there is no perceived need to engage with opposing combat vehicles. The Dingo (UK) and BA-64 (USSR) were typical examples during World War II, while post-war examples include the BRDM series (USSR) as well as the Ferret (UK).
Armored Reconnaissance Vehicle (ARV): The term armored reconnaissance vehicle is typically used for vehicles with similar roles as armored or scout cars but which are tracked rather than wheeled, such as the Scimitar and Scorpion (UK). In size and function, they are the post-war equivalents to World War II-era light tanks and it is not uncommon to see them referred to as such. Additionally, the term may be used for vehicles that rely more on electronic and optical sensors which allows them to maintain some distance from opposing forces. In many cases, these borrow the chassis of APCs making them larger than an armored car, typically 8x8 if wheeled as in the case of the Luchs (Germany) or the M1127 reconnaissance version of the Stryker (US). Nevertheless, there is considerable overlap between these vehicle types, which is further blurred in smaller designs like the Fennek (Germany).
Self-Propelled Gun (SPG): A self-propelled gun is an artillery piece mounted on an vehicle chassis, thus offering it a major improvement in mobility compared to their horse- or truck-towed counterparts and eliminating the need to be unlimbered and set up in their firing positions. Although the concept was introduced in World War I, it was not until World War II when SPGs saw more widespread service although they still represented a minority of artillery on the battlefield. It was only until later in the Cold War that most major armies transitioned to SPGs as their main type of artillery, with notable examples being the 155-mm M109 (US) which saw widespread use among NATO armies as well as the 122-mm 2S1 and 152-mm 2S3 (USSR). Despite resembling tanks in size and shape, SPGs typically have very light armor and modest defensive firepower, usually no more than a machine gun. Some World War II-era Soviet assault guns, however, blurred the line with SPGs, being heavily armored and frequently employed as tank destroyers. However, a key distinction is that an SPG is primarily an indirect fire weapon operating behind the front lines whereas an assault gun is used for direct fire, hence the need for greater protection. SPGs are often differentiated as self-propelled (field) guns or self-propelled howitzers depending on the type of weapon. In practice, almost all SPGs are 'gun-howitzers' given that modern artillery can typically be used interchangeably for both the field gun (flat trajectory of fire) or howitzer (angled trajectory of fire) roles.
Multiple Rocket Launcher (MRL): Vehicle-mounted rocket launchers were introduced in World War II with the legendary Soviet BM-13 'Katyusha' which consisted of rocket launch rails mounted on a truck. Other wartime designs included the Panzerwerfer (Germany) and the T34 Calliope (US), a conversion of the M4 tank. Most post-war MRL platforms remained truck-mounted although some featured a tracked chassis, notably the US M270 MLRS which was widely adopted among NATO armies.
Mortar Carrier (MC): A similar concept to the SPG and MRL but with a mortar instead. Mortar carriers have been based on many different chassis types including half-tracks (mainly by the US in World War II), tracked vehicles, and wheeled vehicles, these being often based on an existing APC design.
Self-Propelled Anti-Aircraft Gun (SPAAG): Like most forms of artillery, anti-aircraft guns found themselves installed on vehicle chassis beginning in World War II. These could be in the form of machine guns or cannon (often in dual- or quad-mounts) or larger flak guns. Due to Allied air superiority, Germany was a widespread user of SPAAGs which included designs like the Wirbelwind and Ostwind which were easily recognizable thanks to their multi-sided turrets. US SPAAGs were typically mounted on the chassis of M3 half-tracks while British SPAAGs were mounted on Crusader tank hulls. SPAAGs appeared obsolete in the post-war period but found a new lease of life thanks to the Soviet ZSU-23-4 which incorporated a search and track radar and could be linked to other radars and SAMs. A similar Western design is the German Gepard.
Self-Propelled Air Defense (SPAD): A similar concept to the SPAAG but with surface-air-missiles (SAMs) as the primary armament rather than guns. Chassis types vary considerable, and range from light trucks to the hulls of tracked APCs or IFVs. Notable SPAD platforms include the Soviet-built 2K12 (firing SA-6 missiles) which took a toll on Israeli aircraft during the 1973 Yom Kippur War while the US has relied on the M48 Chaparral (Sidewinder missile) based on the M113 chassis and, more recently, the M6 Linebacker (Stinger missile) based on the M2/M3 chassis.
Armored Recovery Vehicle (ARV): Armored Recovery Vehicles (ARVs) are usually variants of an existing tank or APC which have been modified to carry specialized lifting and recovery equipment such as cranes, winches, and bulldozer blades as well as repair equipment. These typically replace the turret or any other main armament although some carry small defensive armament of their own. Given that they retain the protection level of their original design, they are able to operate in combat zones.
Armored Ambulance (AA): Armored Ambulances (AA) are specially modified versions of APCs where the troop compartment serves as a medical facility. These can typically carry around 3-4 stretchers or a larger number of sitting patients. Operating in combat zones, they are mostly used to carry wounded troops to dressing stations or field hospitals.
Armored Bridgelayer (ABL): As the name implies, these are specialized vehicles capable of carrying a folding metal bridge which can be laid down on a river or other obstacle. Because of the weight of the folding bridge and the need to operate close to the front lines, ABLs are usually based on a tank chassis rather than a lighter and more poorly protected APC.
Combat Engineering Vehicle (CEV): This is a generic term for a vehicle capable of undertaking engineering tasks such as mine clearing, obstacle removal, or earth moving. They also include some of the previous categories such as bridgelayers. Probably the most famous examples of these vehicles were "Hobart's Funnies" of the 79th (British) Armoured Division during World War II, which included mine-flaying Churchill and Sherman "Crabs", AVREs, DD amphibious tanks among others.
Artillery Tractor (AT): Also known as a gun tractor, these have been either trucks, half-tracks, or tracked vehicles designed to tow artillery pieces and/or their ammunition as well as transport the artillery crew. The latter generally requires a troop compartment which means that these vehicles can also be used as personnel carriers when required, as was the case with the US M2 half-track as well as the SfKdz 6-11 series of German half-tracks during World War II. Artillery tractors are also given the more generic term of Prime Movers given that they are not limited to towing artillery pieces and many also function as recovery vehicles.