The first highly publicized wave of mysterious things seen in the sky during the modern era was not in 1947, as many people think, but actually in 1896. From November of that year through April of 1897, people were seeing "Phantom Airships", similar to dirigibles (which were, according to many sources, still in the experimental stages); some accounts reported flapping wings, like a giant bird. These craft were widely reported and the press gave it plenty of coverage ( though many of these were deliberate hoaxes by newspapers to increase sales). There seems little doubt, despite the hoaxes, that some people were actually seeing something. But what? Most people at the time thought it was some new flying machine by a cutting-edge inventor. Only one report- now documented as a hoax- attempted to describe "The Airship" as extraterrestrial. There are those who suggest that whatever is at the source of the UFO phenomenon somehow shifts its visible shape to whatever will be best received by those who see it- often something just at the edge of human capability or imagination, preceding the direction of history by a few years.* And there are those who insist that the whole thing can be chalked up to a combination of hysteria and hoax.
*In keeping with this, there were Phantom Airships spotted frequently over Britain between 1909 and 1913; residents thought it was the Germans, spying or planning raids. This did eventually happen after war broke out in 1914, but the idea that there were Zeppelin flyovers prior to WW I is hotly debated.