The sight of Russian tank turrets, blown off and lying in ruin along Ukrainian roads, points to a tank design issue known as the “jack-in-the-box” flaw.

The fault is related to the way many Russian tanks hold and load ammunition. In these tanks, including the T-72, the Soviet-designed vehicle that has seen wide use in Russia’s invasion of Ukraine, shells are all placed in a ring within the turret. When an enemy shot hits the right spot, the ring of ammunition can quickly “cook off” and ignite a chain reaction, blasting the turret off the tank’s hull in a lethal blow.

“For a Russian crew, if the ammo storage compartment is hit, everyone is dead,” said Robert E. Hamilton, a professor at the U.S. Army War College, adding that the force of the explosion can “instantaneously vaporize” the crew. “All those rounds — around 40 depending on if they’re carrying a full load or not — are all going to cook off, and everyone is going to be dead.”