"All the tested drones have safely returned to Russia for studies on their use in hot climates and sandstorms," the source told RIA Novosti.
"The drones that have been used in Syria, not all, but there were quite a lot, flew on hydrogen fuel. In other words, they can stay in the air for a long time, allowing the propulsion to replenish energy," the source said.
According to the source, all UAVs have returned to Russia for analysis of combat data, including performance in sandstorms, FNA reported.
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