KYIV — Sergeant Yegor Firsov, deputy commander of a Ukrainian army strike drone unit, sounds exhausted in a voice message he sent to POLITICO from Avdiivka, an industrial city at the center of intense fighting on the eastern front.

Russian troops have been storming Avdiivka relentlessly for more than two weeks in an all-out effort to encircle the Ukrainian forces there.

“The situation is very difficult. We are fighting for the heights around the city," Firsov said. "If the enemy controls these heights, then all logistics and roads leading to the city will be under its control. This will make it much harder to resupply our forces.”

Facing an enemy with superior numbers of troops and armor, the Ukrainian defenders are holding on with the help of tiny drones flown by operators like Firsov that, for a few hundred dollars, can deliver an explosive charge capable of destroying a Russian tank worth more than $2 million.

The FPV — or "first-person view" — drones used in such strikes are equipped with an onboard camera that enables skilled operators like Firsov to direct them to their target with pinpoint accuracy. Before the war, a teenager might hope to get one for a New Year present. Now they are being used as agile weapons that can transform battlefield outcomes. Others are watching, and learning, from a technology that is giving early adopters an asymmetric advantage against established methods of warfare.

“It's hard to handle the emotion when a drone pilot hits a tank. The whole group and the whole platoon are happy like babies. Infantry units are rejoicing nearby. Everyone is screaming, and hugging. Although they do not know the guy who gave them this happiness,” Firsov wrote in a Facebook post.

A typical FPV weighs up to one kilogram, has four small engines, a battery, a frame and a camera connected wirelessly to goggles worn by a pilot operating it remotely. It can carry up to 2.5 kilograms of explosives and strike a target at a speed of up to 150 kilometers per hour, explains Pavlo Tsybenko, acting director of the Dronarium military academy outside Kyiv.

“This drone costs up to $400 and can be made anywhere. We made ours using microchips imported from China and details we bought on AliExpress. We made the carbon frame ourselves. And, yeah, the batteries are from Tesla. One car has like 1,100 batteries that can be used to power these little guys,” Tsybenko told POLITICO on a recent visit, showing the custom-made FPV drones used by the academy to train future drone pilots.

“It is almost impossible to shoot it down," he said. "Only a net can help. And I predict that soon we will have to put up such nets above our cities, or at least government buildings, all over Europe.”