Of the 31 Abrams tanks the U.S. sent to Ukraine, six have been destroyed, according to Oryx, an independent analyst group that tracks casualties. The rest are now used only occasionally. At $10 million apiece, tanks like the Abrams are not easily replaced. Among other Western tanks sent to Ukraine, 12 of the 18 latest-model German Leopards have been destroyed or damaged, according to Oryx.

As soon as you get on the road, a drone spots you, and then you're being hit with artillery, mines, anti-tank missiles, drones, guided bombs," said a Ukrainian driver of one of the Abrams tanks whose call sign is Smilik.