At a secretive factory in Russia’s central grasslands, engineers are manufacturing hundreds of decoy drones meant to overwhelm Ukrainian defenses as they try to protect against a horrific new weapon, an Associated Press investigation has found.

The plant at Russia’s Alabuga Special Economic Zone recently started churning out thermobaric drones alongside the decoys, the investigation found. The thermobaric warheads create a vortex of high pressure and heat that can penetrate thick walls. They suck out all the oxygen in their path, and have a fearsome reputation because of the injuries inflicted even outside the initial blast site: Collapsed lungs, crushed eyeballs, brain damage.

Russia came up with the plan for decoys in late 2022 and codenamed it Operation False Target, according to a person familiar with Russia’s drone production who spoke on condition of anonymity because the industry is highly sensitive. The idea was to launch armed drones along with dozens of decoys, sometimes stuffed with rags or foam, and indistinguishable on radar from those carrying real bombs. Ukrainian forces must make split-second decisions about how to expend scarce resources to save lives and preserve critical infrastructure.