We're talking about objects that are tracked on radar, photographed, and video taped that are seen traveling at speeds and performing maneuvers that no known air-craft can mimic. These objects are constantly seen defying our known laws of aerodynamics. I've written about multiple instances, there are thousands. For example, here's an article about an incident with the Chilean Air Force, they received a radar return of a UFO equal to the size of ten or more aircraft carriers. They had visual confirmation as well.