Deep underground military bases (D.U.M.B.S) are alleged co-managed facilities by aliens and government services.
While there are military bases worldwide, there are three recognized underground military bases in the United States. The Mount Weather Emergency Operations Center is a Department of Homeland Security installation. This underground base is where vital government officials go in the case of a crisis.
Also, the Raven Rock Mountain Complex and the Cheyenne Mountain Complex are two bases run by the Department of Defense.
All three of these bases can communicate with one another in the event of a national crisis.
Also, there are several nuclear missile silos in the United States. These silos are not necessarily underground bases, but the Space Forces use them to launch intercontinental missiles remotely.
Lastly, the Aquarius Reef Base is an underwater installation run by a university. This facility cooperates with both NASA and the Navy for training and research.