The USAF facility (better known as Area 51) is a remote area of Edwards Air Force Base, within the Nevada Test and Training Range. It is publicly unknown what the base's current primary purpose is, however, based on historical data, it most likely supports the development and testing of experimental aircraft and weapons systems.
The secrecy concerning the base has made it the frequent subject of conspiracy theories and a central component to UFO's. Questions about the site remain unanswered.
(Image credit: commons.wikimedia.org/wiki/File:Area_51_ohne_Legende.png)