It was a familiar and vexing problem: Russian soldiers were using the dense cover of tree lines to prepare to storm the Ukrainian trenches.

“We used a lot of resources to try and drive them out and destroy them,” said Capt. Viacheslav, 30, the commander of the 68th Separate Jaeger Brigade’s strike drone company known as “Dovbush’s Hornets.”

But they could not do so, he said in an interview last month.

So they gave a new weapon a newer twist, attaching thermite-spewing canisters to drones and creating a weapon capable of spitting out molten metal that burns at 4,400 degrees Fahrenheit. Soldiers call them “dragon drones.”

Thermite — which was developed a century ago to weld railroad tracks — is a mixture of aluminum and iron oxide. When ignited, it produces a self-sustaining reaction that makes it almost impossible to extinguish.

It was used to devastating effect in both world wars. In Ukraine, it has been used primarily in artillery shells and hand grenades.

Now it is being attached to drones that sweep over Russian defensive positions, raining burning metal over the enemy before crashing. The flames ignite the vegetation that Russian troops use for cover and burn it out, exposing them and their equipment to direct attack.