Originally Posted by
Thekri
A UFO is a national security threat because it is something flying around, and we don't know what it is. That means you can't rule out that it is something that is potentially harmful to our national interests, so we would like to be able to identify them so we know if we have a problem or not. The end goal is to turn UFOs into specific flying objects, like Aircraft, Weather Phenomena, or whatever. If they are extraterrestrial beings, we would like to know that as well.
To give some idea of the reality of these things, without the sensationalism, your average military airfield detects a couple hundred to a thousand UFOs per day. Because every single thing that is detected on any of the radars or sensors is assigned a tracking number and flight path, so that airplanes don't run into them. Most of these go into broad categories like "Probably a Bird" "Probably Wind-blown debris" "Probably Radar reflection" and are thus never investigated again, because nobody has time to determine if the radar signature that looks suspiciously like a flock of Pigeons is actually a flock of Pigeons. You can't definitively state it WAS Pigeons, because you never verified the contact, but the signature can be explained by pigeons, and thus is assumed to be mundane.
An actual aircraft that cannot be identified is a significantly more serious prospect. The government likes to know what all aircraft in its airspace are doing. Who owns them, where they are going, and what they are doing along the way. So if an aircraft doesn't have a flight plan on record, and you don't know what it is, that is a National Security risk. These are the ones the government is most concerned with.
The last category is actual anomalous signatures that can't be adequately explained with any common explanation. These are the ones that people assume are the entirety of the "UFO" catagory, but is reality a minuscule percentage of them. By definition, we do not know what these are, and contrary to what conspiracy theorists would have you believe, they do not have consistent traits. It is relatively easy to pick a subset of these reports that do share characteristics, but that is just a matter of combing data until you find what you are looking for. From there, the pop culture approach is to recite cherry picked data over ominous music, and then jump immediately to wild speculation. This is not what the military does, and is not helpful to actually figuring out what specific examples are. It is not statistically possible to have one explanation for all these.