Once it is granted that the objects and their detectable properties are real, and not illusions, there are really only a few possibilities.
1) Advanced and highly secretive technology developed by some government.
2) The same, but by a group within our own government, but off-budget and highly secret (think NSA in the bad old days when it didn't officially exist).
3) The same, but by a non-governmental group of industrialists or similar, but still terrestrial.
4) Aliens
Given the occurrence of these phenomena around military deployments, bases, and nuclear facilities, my money's on #1.
Defaulting to aliens seems attractive to those who presume the technology is too advanced, seemingly violating the laws of physics, and thus an exotic explanation is required. This is illogical.
If the objects are real, and (big) if they are violating the laws of physics as we know them, that means that our understanding of physics needs to be revised. Physics is physics. Explaining it as "aliens" doesn't explain anything. If the physics is wrong (or rather, incomplete, which we already know is the case), then there is no reason to presume that some terrestrial group would be incapable of making and leveraging discoveries that would enable it to create these craft/drones.
We are not lacking in historical examples of tremendous technical advances far outpacing the current understanding. Germany, during WWII, made tremendous advances with the jet engine and in rocketry, even in robotic analog guidance systems, that shocked the scientists in the US. To this day, much of what we acquired with Operation Paperclip is still classified. Why? I'm not going to speculate, but there must be a reason we still don't know what all was acquired from the Germans by the US and Russia.
The same thing could happen again. If new physical principles were, at some point, discovered, leveraged, and developed by some group (governmental or otherwise), they have had quite a few decades to improve on it. Think about how far technology and materials science has come in the public arena in the last 50 years. Add in some exotic discoveries, and some group with the resources to leverage them, and a terrestrial explanation becomes quite plausible. No aliens required.