To go coast to coast with those costs would be trillions. And that tunnel wasnt built to be hardened against nuclear attacks, or bunker busters either. If you go deeper it gets more expensive. You need climate control systems to control geothermal heat. You need pumps to keep it from flooding. You need ventilation systems ever so often to bring in air from the surface. You need emergency exits so if part of it collapses people arent trapped inside.

From what I was told, there was all of that. I have zero doubt the U.S can build the infrastructure it needs. You can see the demonstrations of these in Florida or when the U.S Civil Engineers actually decides to do something with a public project; and that's something more commercial/environmental with less manpower and funding.

Will it do it for civilians? Absolutely not. Only for essential/top-demand things in the military. All of the other stuff is handled by private citizens/contractors.

The United States has consistently failed billion+ dollar audits for it's already incredibly labyrinthine defense industry. While I don't doubt that it is mostly grift and corruption, I also don't doubt that the U.S is consistently funneling dark money into horrors and projects like these.

I can absolutely believe for a moment that when it comes to military infrastructure deemed essential and important to the military, it can be built. New technology, R&D however? No. The matter of moving mountains and everything you described can be done with todays technology. I don't believe they're hauling grey aliens across the country in tunnels reaching the mantle/core of the earth in Hyperborea.

I would believe that there are unloading stations with surface-level connections across the country. Not all of it is "Deep underground". There are railroads to military sites and those aren't commonly accessible to the average person. Other people in the military have said similar things about underground access points. It's all anecdotal, of course.