There were some interesting posts by an ATS member back in the day who used to work for federal agencies. She mentioned seeing papers cross her desk in reference to reports of a secret underground maglev "bullet train" network.
I think this was cover for a linear particle accelerator network that took the place of star wars.
The air force did some experiments back in the 80s and found two interesting things. First was that all particle beams in the atmosphere became charged particle beams due to interaction with the air molecules and they all experienced self-pinching behavior which kept the beam focused and on target. Second was that highly energetic particles phase through matter at a predictable rate, allowing energy to be dumped behind heat shielding and other such things.
Combine this with some of the behaviors seen from lights over Area 51 and others, and I am more of the opinion we have a strategic anti-missile and even anti-aerospace system built around a metal ion linear accelerator array.
There again, it could also be some kind of mapping system for satellites or some weird shit only the government could think of doing and have the resources to make it happen.