An array of mostly unremarkable items stretched across two wooden tables on the far side of a cramped workshop in eastern Ukraine: double-sided tape, gloves, Allen wrenches, a soldering iron, 3D-printed plastic, ball bearings, a digital scale. Next to them was a German DM51 fragmentation grenade.

They were all important ingredients for Ukrainian troops trying to piece together a puzzle: How do you create a grenade that weighs next to nothing but can be dropped from a drone and destroy a roughly 40-ton Russian tank?

"War is an economy. It’s money,” said Graf, a stout, bearded Ukrainian soldier in charge of his unit’s drone team. "And if you have a drone for $3,000 (¥396,326) and a grenade for $200, and you destroy a tank that costs $3 million, it’s very interesting.”