"This is a new form of man-made flight," Keennon said. It is about "biomimicry," or building a machine that is inspired by nature, he said.

The Pentagon issued seven specific milestones for the Hummingbird, including the ability to hover in a 5-mph wind gust and the ability to fly from outdoors to indoors and back outdoors through a normal-size doorway.

Critics have noted that privacy issues may emerge depending on how the drones are used.

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