Main battle tank

A main battle tank (MBT), also known as a battle tank, is a tank that fills the role of armour-protected direct fire and maneuver in many modern armies. Cold War-era development of more powerful engines, better suspension systems and lighter composite armour allowed for the design of a tank that had the firepower of a super-heavy tank, the armour protection of a heavy tank, and the mobility of a light tank, in a package with the weight of a medium tank. The first designated MBT was the British Chieftain tank, which during its development in the 1950s was re-designed as an MBT. Throughout the 1960s and 1970s, the MBT replaced almost all other types of tanks, leaving only some specialist roles to be filled by lighter designs or other types of armoured fighting vehicles.

Main battle tanks are a key component of modern armies. Modern MBTs seldom operate alone, as they are organized into armoured units that include the support of infantry, who may accompany the tanks in infantry fighting vehicles. They are also often supported by surveillance or ground-attack aircraft. The average weight of MBTs varies from country to country. The average weight of Western MBTs is usually greater than that of Russian or Chinese MBTs.

History

Initial limited-role tank classes

During World War I, combining tracks, armour, and guns into a functional vehicle pushed the limits of mechanical technology. This limited the specific battlefield capabilities any one tank design could be expected to fulfill. A design could have good speed, armour, or firepower, but not all three together.

Facing the deadlock of trench warfare, the first tank designs focused on crossing wide trenches, requiring very long and large vehicles, such as the British Mark I tank and successors; these became known as heavy tanks. Tanks that focused on other combat roles were smaller, like the French Renault FT; these were light tanks or tankettes. Many late-war and inter-war tank designs diverged from these according to new, and mostly untried, concepts for future tank roles and tactics. Each nation tended to create its own list of tank classes with different intended roles, such as "cavalry tanks", "breakthrough tanks", "fast tanks", and "assault tanks". The British maintained cruiser tanks that in order to achieve high speed and hence manoeuvrability in the attack carried less armour, and infantry tanks which operating at infantryman pace could carry more armour.

Evolution of the general-purpose medium tank

After years of isolated and divergent development, the various interwar tank concepts were finally tested with the start of World War II. In the chaos of blitzkrieg, tanks designed for a single role often found themselves forced into battlefield situations they were ill-suited for. During the war, limited-role tank designs tended to be replaced by more general-purpose designs, enabled by improving tank technology. Tank classes became mostly based on weight (and the corresponding transport and logistical needs). This led to new definitions of heavy and light tank classes, with medium tanks covering the balance of those between. The German Panzer IV tank, designed before the war as a "heavy" tank for assaulting fixed positions, was redesigned during the war with armour and gun upgrades to allow it to take on anti-tank roles as well, and was reclassified as a medium tank.

The second half of World War II saw an increased reliance on general-purpose medium tanks, which became the bulk of the tank combat forces. Generally, these designs massed about 25–30 t (25–30 long tons; 28–33 short tons), were armed with cannons around 75 mm (3.0 in), and powered by engines in the 400–500 hp (300–370 kW) range. Notable examples include the Soviet T-34 (the most-produced tank at that time) and the US M4 Sherman.

Late war tank development placed increased emphasis on armour, armament, and anti-tank capabilities for medium tanks:

• The German Panther tank, designed to counter the Soviet T-34, had both armament and armour increased over previous medium tanks. Unlike previous Panzer designs, its frontal armour was sloped for increased effectiveness. It also was equipped with the high-velocity long-barreled 75 mm KwK 42 L/70 gun that was able to defeat the armour of all but the heaviest Allied tank at long range. The powerful Maybach HL230 P30 engine and robust running gear meant that even though the Panther tipped the scales at 50 t (49 long tons; 55 short tons) – sizeable for its day – it was actually quite manoeuvrable, offering better off-road speed than the Panzer IV. However, its rushed development led to reliability and maintenance issues.
• The Soviet T-44 incorporated many of the lessons learned with the extensive use of the T-34 model, and some of those modifications were used in the first MBTs, like a modern torsion suspension, instead of the Christie suspension version of the T-34, and a transversally mounted engine that simplified its gearbox. It is also seen as direct predecessor of the T-54 Unlike the T-34, the T-44 had a suspension sturdy enough to be able to mount a 100 mm (3.9 in) cannon.
• The American M26 Pershing, a medium tank of 40 short tons (36 t; 36 long tons) to replace the M4 Sherman, innovated in US tanks many features common on post-war MBTs. These features include an automatic transmission mounted in the rear, torsion bar suspension and had an early form of a powerpack, combining an engine and transmission into a compact package. The M26, however, suffered from a relatively weak engine for its weight (effectively the same engine as the 10 t (9.8 long tons; 11 short tons) lighter M4A3 Sherman), and as a result was somewhat underpowered. The design of the M26 had profound influence on American postwar medium and main battle tanks: "The M26 formed the basis for the postwar generation of US battle tanks from the M46 through the M47, M48, and M60 series."

British universal tank

Britain had continued on the path of parallel development of cruiser tanks and infantry tanks. Development of the Rolls-Royce Meteor engine for the Cromwell tank, combined with efficiency savings elsewhere in the design, almost doubled the horsepower for cruiser tanks. This led to speculation of a "Universal Tank", able to take on the roles of both a cruiser and an infantry tank by combining heavy armour and manoeuvrability.

Field Marshal Bernard Montgomery is acknowledged as the main advocate of the British universal tank concept as early as 1943, according to the writings of Giffard Le Quesne Martel, but little progress was made beyond development of the basic Cromwell cruiser tank that eventually led to the Centurion. The Centurion, at the time designated "heavy cruiser" and later "medium gun tank" was designed for mobility and firepower at the expense of armour, but more engine power permitted more armour protection, so the Centurion could also operate as an infantry tank, doing so well that development of a new universal tank was rendered unnecessary.

The Centurion, entering service just as World War II finished, was a multi-role tank that subsequently formed the main armoured element of the British Army of the Rhine, the armed forces of the British Empire and Commonwealth forces, and subsequently many other nations through exports, whose cost was met largely by the US. The introduction of the 84 mm (3.3 in) 20-pounder gun in 1948 gave the tank a significant advantage over other tanks of the era, paving the way for a new tank classification, the main battle tank, which gradually superseded previous weight and armament classes.

Cold War

A surplus of effective WWII-era designs in other forces, notably the US and the Soviet Union, led to slower introductions of similar designs on their part. By the early 1950s, these designs were clearly no longer competitive, especially in a world of shaped charge weapons, and new designs rapidly emerged from most armed forces.

The Quebec conference in 1957 between the US, UK and Canada identified the MBT as the route for development rather than separate medium and heavy tanks.

The concept of the medium tank gradually evolved into the MBT in the 1960s, as it was realized that medium tanks could carry guns (such as the American 90 mm (3.5 in), Soviet 100 mm (3.9 in), and especially the British L7 105 mm (4.1 in)) that could penetrate any practical level of armour then existing at long range. Also, the heaviest tanks were unable to use most existing bridges. The World War II concept of heavy tanks, armed with the most powerful guns and heaviest armour, became obsolete because the large tanks were too expensive and just as vulnerable to damage by mines, bombs, rockets, and artillery. Likewise, World War II had shown that lightly armed and armoured tanks were of limited value in most roles. Even reconnaissance vehicles had shown a trend towards heavier weight and greater firepower during World War II; speed was not a substitute for armour and firepower.