What is a Main Battle Tank?

With a major war on ithat seems to be escalating all the time a great deal of military terminology is being tossed about with little or no explanation--and often great inaccuracy. One hears of "armored fighting vehicles, "tanks," "main battle tanks"--and unless they have some knowledge of their own are not sure whether these things are synonymous or not (the more in as some use them interchangeably).

One should start with the most general category--"armored fighting vehicle." As the name indicates this refers to just about any kind of armored vehicle used in combat.

The term "tank" is much more specific. It specifically refers to tracked vehicles with a large gun used for direct fire (shooting straight at targets the crew can see) as their main armament (in contrast with self-propelled artillery where the crew rides in an armored cabin, which can look a lot like a tank, as with the M109 Paladin, but are used for indirect fire, firing its bigger gun at targets outside the crew's line of sight). Unlike an armored personnel carrier (like the M113) or infantry fighting vehicle (like the M2 Bradley) tanks also do not carry troops. They also tend to be much more thickly armored (where a personnel carrier or infantry fighting vehicle has the equivalent of an inch or so of steel in its best-protected areas, current-generation tanks have the equivalent of two feet or more), have a bigger gun (the M2 Bradley having a gun, but just a 25 mm auto-cannon not intended for fighting a full-blown tank the way that an Abrams can), and be heavier than those vehicles (a Bradley weighing about 28 tons, an Abrams as much as 70+ depending on the model).

The term "main battle tank" refers to how the tank developed after World War II. In the preceding period, extending through that conflict, armies tended to use a combination of tank types specialized for different roles. There were light tanks, heavy tanks and medium tanks--with the schematic explanation that the lightly armored and gunned but highly mobile light tanks used for scouting, heavily armored and gunned but not so mobile heavy tanks called up to make the big breakthroughs, and medium tanks striking a balance between the two were used for exploiting those breakthroughs.* (In the World War II-era American army the M2s were the light tanks, the M26 Pershings the heavy tanks, the M4 Shermans the medium tanks.)

By contrast the "main battle tank" (whose potential was displayed by relatively balanced wartime designs like the Soviet T34) replaced the three types with a single, "universal" tank from the late 1940s on.** It did not do so immediately and completely, many countries continuing to produce light tanks long after adopting the main battle tank--the Soviets, for instance, continuing to use PT-76s they introduced the T-54 and later main battle tanks, while at an even later date Britain produced the Scorpion light tank alongside its heavier Chieftain main battle tanks. Some interest also remained in light tanks for the purpose of equipping light forces, like the M551 Sheridan used by the U.S. 82nd airborne division (and the M8 Armored Gun System intended to replace it, but ultimately canceled). Additionally even after the light tank was generally set aside the major armies still produced light, reconnaissance-oriented armored vehicles, some of them with big guns (as with France's AMX-10RC reconnaissance vehicles, which are frequently being referred to as "tanks" these days, in spite of their having wheels and not tracks). Still, the main battle tank filled more of the niches than any of the earlier types did, and if lighter armored vehicles were still part of the mix, those performing the scout role tend to not be of the light tank type (the U.S., for example, using the M3 version of the Bradley), while they tend to not field anything heavier (no super-heavy counterpart to the Abrams existing). All of this has some reflection in the fact that the term "tank," to the extent that the term is not simply used to refer to any old armored vehicle, is synonymous with main battle tanks now.

* In practice it was not always so clear-cut--some armies making little use of light tanks (like the British, who preferred armored cars for scouting), others little use of heavy tanks (like the U.S. Army, the Pershing coming in fairly light as the medium Shermans proved the workhorse of the war). The reader may also note that light tanks were sometimes called "infantry tanks," medium tanks "cruiser tanks"--the latter reflecting their being thought of like "land warships," with cruisers relatively agile, medium-sized vehicles operating independently from a larger fleet (with light tanks the "scout cruisers" and the heavy tanks the "battleships" of the fleet).
** The T-34 owed its success in part to its mass-reproducibility, but also that balance of mobility, protection and firepower, in which it was helped by the innovations it incorporated--among them the then-novel use of a diesel engine and Christie suspension, and "sloped armor," which by putting an armor plate at an angle to the likely direction from which fire would come, forced an incoming shell to pass through a greater thickness of steel.