As we get into the Cold War era, one thing becomes simpler: the distinction between different kinds of tanks (heavy, medium, light, cruiser, infantry, etc) largely drops away. Improved engines, suspension and lighter but more effective composite armor meant that the slightly different roles of the different weights of tank could increasingly be accomplished by a single platform evolving out of late-war medium tanks. You could now fit a heavy tank’s gun and armor on a chassis with a medium tank’s speed and maneuverability. The first of these “universal” tanks was the British Centurion (first deployed in 1945 [but did not see WW2 combat]) and other countries followed suit.

The result is the modern “main battle tank” (MBT), typically between 45 and 75 tons, with a single powerful direct-fire cannon as its primary armament. That’s not to say design differences between militaries drop away; there are still decisions to be made: the level of emphasis between speed, armor and firepower for instance. Another major decision is whether a tank is designed with a three-person turret (one of whom is a dedicated loader) or a two-person turret with an autoloader (that is, a machine that does the loading for you). It used to be that now I’d have to go on about why going autoloaders aren’t simply obviously the best but given the live demonstrations of some of the drawbacks of Soviet/Russian carousel autoloaders going on right now [in Ukraine] I’ll just say that both options have advantages and drawbacks and move on. So there is variety within the idea of an MBT, but by and large most countries field just one type of MBT (or one family of MBTs for countries which can’t afford to retire older systems) and that covers their tank needs.

But of course nothing could easy so just as tanks were getting easier to keep track of, APCs get much more complicated. Even before they were fully enclosed, APCs had generally carried some kind of defensive weapon (usually a heavy machine gun), but you weren’t supposed to fight with it if you could avoid it. Beginning in the 1950s, designers – first in West Germany – began experimenting with the idea that an APC could be armed to not merely deliver the infantry (“dismounts”) but to actually fight when they got there. The thing is, there are a lot of situations where an infantry formation might want more firepower but where a tank would be overkill: armored vehicles lighter than tanks, or enemies with lighter fortifications, for instance. West Germany pioneered the idea by putting a 20mm autocannon on their APC, the Schützenpanzer Lang HS.30, enabling it to put out some meaningful firepower, albeit much less than a tank.

The USSR cottoned on to the idea and liked it, resulting in the Soviet BMP-1 and the subsequent BMP family of what we call “infantry fighting vehicles” (IFV). Initially resistant to the idea (American doctrine was that APCs move troops and should not fight if they could help it), the United States, noticing the effectiveness of these sorts of platforms, got into the act with the Bradley Fighting Vehicle (these days the M2 Bradley). And IFVs, especially the Bradley, look like tanks. And indeed, they are sometimes called on to do the kind of armored reconnaissance and infantry support jobs that in a previous era would have gone to a light tank.

But they are also notably not tanks in several key ways. The primary job of an IFV is to move infantry and support them against lighter targets; some IFVs do maintain some kind of anti-tank capability, but it tends to be more limited (e.g. the Bradley’s pair of TOW AT missiles). The requirement that an IFV needs to be fairly fast but also needs to fit a bunch of dismounts means they can’t carry the firepower or the armor of a tank, often using lighter aluminum armor rather than steel or heavy composites. Finally, the tendency is for IFVs to mount lighter primarily armaments – again, space and weight concerns – like the Bradley’s 25mm M242 Bushmaster chain gun. The BMP-3 is probably the most heavily armed IFV out there with a low-velocity 100mm rifled gun and a 30mm autocannon, which is still a far cry from the firepower of the high-velocity 125mm main gun of a contemporary T-80 or the 120mm high velocity gun of a M1A1 Abrams. Instead, most IFVs would rely on anti-tank missile systems to engage tanks (although IFV autocannons can cause a tank serious problems if they can engage the rear or side armor, which is thinner).

Note that the IFV did not mean the end of the APC just as the APC didn’t bring the end of soft-skinned troop transports. In the US military, the Bradley serves alongside lighter-but-still-IFV Strykers, the venerable M113 APC along with soft-skinned HMMWV (Humvees; to be in theory replaced with the Oshkosh L-ATV) and trucks of various kinds and uses. Likewise, the Russian army has its BMPs (which are IFVs), and BTRs (which are APCs) as well as soft-skinned vehicles – or at least it did until, I am now being told, they were all towed away by Ukrainian farmers. The real Iron Harvest.

The final category worth noting here are variations on the concept of the MRAP (Mine-Resistant, Ambush-Protected): infantry transport vehicles designed to resist the sort of dangers one encounters in counter-insurgency operations, mostly mines, IEDs and small-arms ambushes. In essence, these vehicles are a purpose-built version of the up-armored Humvees designed to operate in a very particular combat environment (insurgencies and particularly urban insurgencies). These sort of vehicles have gotten more visibility in the United States because many of them have been shifted into the hands of law enforcement, where their utility is questionable, to say the least.

Bret Devereaux, “Collections: When is a ‘Tank’ Not a Tank?”, A Collection of Unmitigated Pedantry, 2022-05-06.