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Napoleon's soldiers used them. So did Union troops in the Civil War. Peter Bergen recalls that his father worked in the US Air Force on a project that sent camera-equipped balloons over the Soviet Union. The balloon that floated over the US was not a national security catastrophe, as some Republicans suggested, but a reminder of the espionage threats facing the country, Bergen says.

Some earlier incidents had been classified as unexplained phenomena and handed over to a Pentagon task force charged with investigating U.F.O.s.

When President Joe Biden first learned a likely Chinese spy balloon was drifting through the stratosphere 60,000 feet above Montana, his first inclination was to take it down.

Peter Bergen and writer Erik German unpack the US Office of the Director of National Intelligence's latest report about "Unidentified Aerial Phenomena" -- or UFOs.

All the secrets about UFOs you need to know.