Surrounded by rooms filled with stacks of cluster munitions and half-made thermobaric bombs, a soldier from Ukraine’s 92nd Mechanized Brigade recently worked on the final part of a deadly supply chain that stretches from China’s factories to a basement 5 miles from the front lines of the war with Russia.

This is where Ukrainian soldiers turn hobbyist drones into combat weapons. At a cluttered desk, the soldier attached a modified battery to a quadcopter so it could fly farther. Pilots would later zip-tie a homemade shell to the bottom and crash the gadgets into Russian trenches and tanks, turning the drones into human-guided missiles.

The aerial vehicles have been so effective at combat that most of the drone rotors and airframes that filled the basement workshop would be gone by the end of the week. Finding new supplies has become a full-time job.