The Ukrainian soldier swore and tore off his headset. His video monitor had gone blurry at first, the landscape of shattered trees and shell craters barely visible, before blacking out completely. The Russians had jammed the signal of his drone as it was flying outside the town of Kreminna in eastern Ukraine.

“Some days everything goes smoothly, other days the equipment breaks, the drones are fragile and there is jamming,” said the soldier, who goes by the call sign DJ and was speaking from his underground outpost a few miles from the front line.

For a while, the Ukrainians enjoyed a honeymoon period with their self-detonating drones that were used like homemade missiles. The weapons seemed like an effective alternative to artillery shells for striking Russian forces.

Now, the bad days are starting to outweigh the good ones: electronic countermeasures have become one of the Russian military’s most formidable weapons after years of honing their capabilities.

Electronic warfare remains a hidden hand in much of the war, and like Ukraine’s disadvantage in troop numbers and ammunition supplies, Ukraine suffers in this area as well in comparison to Russia. Russia has more jamming equipment capable of overpowering Ukrainian signals by broadcasting on the same frequencies at higher power. It also exhibits better coordination among their units.