The existence of DUMBs (Deep Underground Military Bases) has been discussed for many years in many forums, some a little whacky and some well sourced. There is enough information about them out there that I am not averse to the notion that there are lots of them in the US. A quick search came up with this link, for example:
https://www.intellihub.com/do-deep-underground-military-bases-exist/
There is lots more info out there for those who want to research and decide. I view it as interesting and something to be aware of.
Word is there is one under the Capitol building or nearby buildings in Washington D.C.
Interesting times indeed...