[Sticking only with verifiable occurrances, easily verified via the Blue Book documents, and all of the other Links I added to my blog]
1. Since at least the earliest parts of the 1900s, but maybe even the late 1800s (depending upon how many of these were early dirigibles), weird reports of other-worldly aeroships began to cross into reality, as if magically wrestled from the pages of some sci-Fi comic. UFOs erupted into our collective consciousness, especially,in 1947, after Kenneth Arnold's sighting drew so much attention.
2. From thne beginning there have been countless claims of reports of "Impacts" of an Unkown objects with the earth. Even with the more robust cases, official information, regarding the details of these, is always lacking.
3. reports of occupants emerged along side with object sightings, though it is under reported in most of the history.
4. reports of sightings, and differing levels of contact, have risen steadily with the history of the phenomenon
5. Years, and years of study have shown that our interceptors have chased countless numbers of UFOs (as in Unknown Aero Ships, rather than just unknown enemy aircraft) and it was always futile. Several cases have caused statements like: "It left into outer space", or "it went straight up, out of sight."
6. The psychological Warfare aspect of this phenomenon has been utilized by some apparatus in such a way as to have made it nearly impossible for anyone to be able to arrive at any solid truth regarding these phenomena, and their origin.
7. You don't disclose what is currently regarded as important, and secret.