There's a problem with Russia's tanks—one born out of a design decision that was intended to make them better. As Forbes explains in detail, Russia's T-72 series and subsequent tanks trade the traditional four-man set-up for a design that only requires three crewmembers by automating the role of the loader. That means less manpower is needed to operate the tank, and it reduces the size of the turret. That makes the tank shorter and, among other things, a bit harder to hit. But as CNN reports, when they are hit, things can go very wrong because of that very design. It relates to the way ammunition is stored; to facilitate the automatic loading, there are multiple shells in the turret.
"Even an indirect hit can start a chain reaction that explodes their entire ammunition store of up to 40 shells," CNN explains. The blast can pack enough force to send the tank's turret up to two stories into the air, turning the crew into easy targets. As a defense industry analyst puts it, "If you don't get out within the first second, you're toast." But the crux of CNN's report isn't that the design exists: It's that it has existed for so long—the West has been aware of it since the Gulf War—and so Moscow should have known it would once again prove problematic; it's believed between 300 and nearly 600 of Russia's tanks have been destroyed in Ukraine.
How many lives have been lost is unclear, but the manpower isn't easy to replace: Training tank crews is a time-consuming task that typically takes months at a minimum. The T-72 tanks may not just be an issue for Russia, though. Defense News reports Poland's prime minister confirmed this week that it has delivered some of its Soviet-designed T-72 tanks to Ukraine; the Financial Times reports the Czech Republic has supplied the country with T-72 tanks as well. Though as Forbes previously noted, much of the Ukraine's own "combat power currently seems to be in the form of light infantry teams armed with anti-tank weapons." (More Russia-Ukraine war stories.)