RAF FAIRFORD, England—Ukraine has a network of almost 10,000 acoustic sensors scattered around the country that locate Russian drones and send targeting information to soldiers in the field who gun them down. 

Dubbed “Sky Fortress,” the concept was developed by two Ukrainian engineers in a garage who put a microphone and a cell phone on a six-foot pole to listen for one-way UAVs, said Gen. James Hecker, commander of U.S. Air Forces in Europe and Africa. 

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