The drones began crashing on Ukraine’s front lines, with little explanation. For months, the aerial vehicles supplied by Quantum Systems, a German technology firm, had worked smoothly for Ukraine’s military, swooping through the air to spot enemy tanks and troops in the country’s war against Russia. Then late last year, the machines abruptly started falling from the sky as they returned from missions. “It was this mystery,” said Sven Kruck, a Quantum executive who received a stern letter from Ukraine’s Ministry of Defense demanding a fix. “All we could do is get information from the operators, try to find out what wasn’t working, test and try again,” Mr. Kruck said.

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Persons: ”, Sven Kruck, ” Mr, Kruck Organizations: Quantum Systems, Russia, Ukraine’s Ministry of Defense Locations: German