Everybody except journalists knows what a tank is, yet it is difficult to define. So what is a tank?

Google is not much of a help; asking it produces a definition that a tank is “a heavy armoured fighting vehicle carrying guns and moving on a continuous articulated metal track”. But that definition would include heavily armored tracked APCs such as Namer. And of course, there is the following chart:

Problem with this is that any definition either includes or excludes much of what are considered tanks in modern parlance. At ACOUP blog, Bret provides a definition that “a tank is a heavily armored and tracked combat vehicle whose purpose is to offer powerful direct fire capabilities against a range of enemy targets”. But this definition too is lacking: in fact, it is just as applicable (if not more so) to an assault gun than it is to a tank. In fact, many tanks were not that heavily armored. And on the opposite side, the purpose of an assault gun is specifically provision of direct fire support against a range of enemy targets, and its purpose means that it typically is very heavily armored.

So what is a tank?

Origins of the Tank

Tank originated out of the need to solve the stalemate of the First World War’s Western Front. There were many attempts to do so by various means, but neither the specialized assault troops nor improved artillery techniques were successful (and neither would be the tanks, for the same reasons as all of the previous failed: logistics were dependant on railroad, which meant that defender could reinforce far more quickly than the attacker).

Germans decided to solve the issue by simply producing even more gun, but the British had a different idea. Lieutenant Ernest Swinton, a British military analyst, was sent to the Western Front to assess the situation. His conclusion was that the breakthrough could be achieved with a Holt tracked tractor with added armor for protection against bullets. Maurice Hankey, a secretary of the Committee of Imperial Defence, forwarded his idea to Churchill, adding that armored tractor could also mount the Maxim machine gun. On 13^th January members of the Committee had a ride in the tractor, and on 20^th January Swinton’s idea was officially accepted. In order to maintain secrecy, new vehicle had a name “tank”.

Basic requirements were dictated by realities of the Western Front. New vehicles had to be able to deliver direct fire to enemy positions, resist return fire, cross trenches and barbed wire, to move on a muddy, artillery-plowed fields, climb a parapet and then cross a trench. Thus a clear trinity of firepower – armor – mobility has emerged from the beginning of the tank design. Armored protection and relatively heavy firepower combined with need to cross soft ground meant that tank had to use tracks as to achieve as low as possible ground pressure despite its significant weight. And tanks are heavy. Even a light World War I tank such as Renault FT weighted 6,5 metric tons, while a heavy tank such as British Mark I weighted over 28 tons.

This meant that tires were a no-go: such a heavy vehicle would sink into the ground at anything other than a hard road. Luckily, farming tractors were also heavy and designed to operate in conditions quite similar to what tanks would be facing. And heaviest tractors could be quite heavy, and utilized continuous tracks or treads to solve the problem. So while tracks are not necessarily part of the definition of the tank, other aspects of the tank design pretty much necessitate usage of tracked drive section (at least until antigravity or something is designed).

Tanks also made use of the numerous light field guns that had been designed for maneuver warfare that had been expected before the war. And while these guns still served well on the Eastern Front in many areas, in the West they had been replaced by the indirect, long-range heavy artillery. Direct fire capability was useless against dug-in troops, and such cannons could be engaged even by rifle and machine gun fire.

But direct fire cannons could still be vital for suppression – if they could be brought close enough. A mobile armored platform (a tank) could do this, with early tanks being either male (carrying artillery) or female (carrying machine guns), but ending with hybrid designs.

When it comes to technical characteristics, thus, tank is defined by the following:

• direct firepower to support the infantry and/or engage enemy vehicles
• enough armor to resist enemy small arms fire
• enough mobility to cross the battlefield

This was not the end of the evolution of the basic concept of tank by far. By early World War II, light tanks were at 5 – 10 tons, medium tanks were around 20 – 25 tons, and heavy tanks anywhere between 25 and 45 tons. However, division here was more a question of tactical role than weight: medium tanks were meant for maneuver while heavy tanks were designed for breakthrough. Because of this, some medium tanks such as German Panther weighted more than heavy tanks of the same generation.

In all cases, the main question was a tradeoff between speed, firepower and armor. British divided their tanks into “cruiser” tanks which emphasized speed and “infantry” tanks which emphasized armor. Other countries divided their tanks into light, medium and heavy tanks. Light tanks were designed with mobility focus: they were intended as scouts, and thus had to be light and fast – but this means that their firepower and armor were limited. Heavy tanks were designed to break through the enemy defences, especially fixed defences, which led to firepower and especially armor being emphasized at the cost of mobility. Medium tanks generally attempted to provide the balance as they were expected to engage in maneuvering combat against enemy tanks. However, the war also saw appearance of tanks that would straddle the line between medium and heavy tanks and thus could be considered protoypes of main battle tanks. Good example is German Panther, which combined powerful gun, heavy armor and high speed, though a true main battle tank would have to wait until British Centurion which was specifically designed to replace both cruiser and infantry tanks.

Differences in design, categorization and focus were driven by differences in tank doctrine. There were fundamental similarities in most countries’ doctrines, in that tanks were supposed to support infantry. Even Germany, country that is believed to have created the modern mobile armored warfare doctrine, still had tanks designed specifically for infantry support. However, that is where similarities ended. France itself was still doctrinally stuck in World War I. French doctrine of “Methodical Battle” assumed infantry will attack on foot with tanks supporting the infantry, and being distributed throughout infantry formations. This led to heavily armored and relatively heavily armed tanks that were slow, with limited range, one-man turret and no radios.

At the opposite end were German maneuver warfare (“Bewegungskrieg”) and Soviet Deep Battle (“glubokaya operatsiya”) doctrines. These doctrines envisioned concentrating tanks into powerful, mobile formations capable of fast movement and complex maneuvers. For this to happen, tanks had to have organic support from other arms: that is, each tank formation had to have its own infantry, artillery and anti-air units, and all of these had to be able to keep up with tanks. This however meant that trucks were no longer sufficient for infantry transport, and therefore specialized tracked vehicles had to be available.

Not-Tanks: Mechanized Infantry and Artillery

During World War II, such “battle taxis” were mostly half-tracks, though some tracked vehicles were also used. Their use was the same as that of modern APCs: they would bring infantry to the edge of the combat area, where infantry would dismount and support tanks in the attack. Reason why half-tracks were popular were simple logistics: driving a tank had to be learned, but everybody who know how to drive a car or a truck could also drive a half-track. Half-tracks were also often adopted from existing trucks. However, open-topped half-tracks were vulnerable to air bursts, and while they could go off-road, their cross-country capability was nowhere as good as that of a tank. Thus half-tracks began to be replaced with fully-enclosed Armored Personnel Carriers.

Fully-enclosed APCs were sometimes tracked and sometimes wheeled, and to a lay person (or a journalist) basically look like a tank. But most of these vehicles are not armored to stick in the fight like a tank, though this might be slowly changing. And while some APCs are heavily armored, and IFVs (Infantry Fighting Vehicles) can have heavy firepower, their main duty is to transport infantry which then can be deployed to support tanks in the attack. To do this, either armor, firepower, or both, have to be sacrificed, and thus they are not capable of fulfilling tank’s roles.

But in order to implement a combined-arms maneuver doctrine, it wasn’t enough to allow just infantry to keep up with tanks. Artillery had to be able to keep up as well. In early World War II, artillery still remained towed artillery designed for, essentially, World War I: horses or trucks would tow it into position and artillery piece would then deploy and remain there for the duration, until moving to the next fire base. But because such pieces could not keep up with tanks, self-propelled artillery made an appearance.

Self-propelled artillery likewise could be direct fire and indirect fire. Tank destroyers are the most obvious type of direct-fire self-propelled artillery, though they got phased out over time as guided anti-tank missiles (ATGM) made long-barelled guns not an only choice for anti-tank work. Tank destroyers however are not tanks, even if they have a turret: their role is to support tanks. Other types of direct-fire self-propelled artillery also existed (such as German assault guns), but the role is today mostly taken up by main battle tank due to its flexibility. Assault guns likewise are not tanks; while their role is similar to that of infantry tanks, and some were turreted as well, assault guns utilized low-velocity cannons that were designed specifically for infantry support whereas infantry tanks still had the capability to engage enemy tanks.

On the contrary, the role of indirect-fire self-propelled artillery only increased over time. Whereas conventional howitzer could not be repositioned to avoid counter-artillery fire, a self-propelled howitzer can fire a round and then immediately reposition to avoid the counter-battery fire, in what is called a shoot-and-scoot maneuver (or “fire-and-displace”). Because self-propelled artillery engages via indirect fire, where shell falls onto the target from above and target itself may not even be visible from the gun’s position, its armor is much thinner as it is designed to defend only against shell fragments and high-explosive shells, not anti-tank weapons.

Main Battle Tanks and APCs

Advancement of propulsion, armament and armor during and after World War II meant medium tanks eventually evolved into what is today known as the “main battle tank”: a hybrid of characteristics of the medium and heavy tanks, combining medium tank’s speed and agility with heavy tank’s armor and firepower. While German Panther might be considered a precursor, first proper main battle tank is British Centurion.

These tanks still have differences in emphasis between the armor, speed and firepower, but these differences are much smaller than between the light, medium and heavy tanks. Differences that do exist are a result of different countries’ requirements as well as strategic and geographic environment. Majority of main battle tanks are between 45 and 75 tons, with the main gun in 120 mm range, loaded either by a human loader or the autoloader. French Leclerc uses conveyor / bustle autoloader, which is just as safe as a human-loaded system as the ammunition is in bustle separate from the crew compartment and equipped with blowout panels. But Soviet style carousel autoloaders are prone to violently blowing up the tank when hit, as was demonstrated during the 1990s wars in Iraq and Yugoslavia, 2003 war in Iraq and the current war in Ukraine.

Meanwhile, APCs got much more complicated. While even early APCs carried some sort of weapon – usually a machine gun – during 1950s designers in West Germany started to look into APC as a platform for providing direct fire support to infantry. Result was Schützenpanzer Lang HS.30, an APC armed with 20 mm autocannon. Soviets adapted the idea into their BMP family of Infantry Fighting Vehicles. United States initially resisted the idea, but then did a quick 180 and designed Bradley. These IFVs have largely taken over the roles of reconnaissance and infantry support that previously had been undertaken by light tanks.

However, even compared to light tanks, IFVs are disadvantaged in some areas, all of which comes down to need to carry infantry. They need to be reasonably fast, carry infantry, and have enough ammunition for autocannon to provide meaningful support. But they cannot carry a large number of infantry compared to dedicated APCs: 25-ton M2 Bradley can carry 6 infantrymen compared to 15-ton FV432 which can carry 10 infantrymen. Need to carry infantry and maintain speed also means that both armor and firepower get compromised compared to a light tank of similar weight. British FV101 Scorpion light tank has heavier firepower (76 mm vs 25 mm), albeit lighter armor, and is almost twice as fast as M2 Bradley, despite weighting 8 tons to Bradley’s 25 tons. Stingray light tank meanwhile has heavier firepower (105 mm vs 25 mm), comparable armor (23 mm steel vs spaced armor offering 14,5 mm protection), comparable speed (70 kph vs 64 kph) and identical range (480 km). Compared to firepower and protection of main battle tanks, IFVs simply cannot compete.

All of this means that while light tanks are generally not used anymore, IFVs did not, could not and will not replace APCs or tanks.

What is a Tank

Overall, role of tanks has stayed mostly the same as it was in World War I:

• provide firepower support to allow infantry to advance
• seize ground and maneuver in environment hostile to infantry
• utilize maneuver to create and exploit breakthrough opportunities
• engage other vehicles and fortified positions
• maintain ability to engage a wide range of ground targets

All of this means that tanks have to have heaviest armor and the main gun possible (within other limitations), which precludes them from carrying out other duties such as infantry transport. This requirement for heavy firepower, armor and mobility likewise requires tanks to be tracked vehicles, otherwise tank would end up in a mobility suicide as wheels would sink into the ground.

Thus, technological definition would be “an armored, tracked vehicle with heavy direct-fire artillery (a.k.a. large-calibre main gun), designed to engage a wide variety of ground targets while utilizing fire and maneuver to carry out combat tasks or to assist other units in carrying out their tasks”.

• modern
• technology
• weapons