The Raven Rock Mountain Complex, also known as Site R, is a U.S. military installation with an extensive underground nuclear bunker located near Blue Ridge Summit, Pennsylvania. Built in the early 1950s during the Cold War era, this facility serves as a Continuity of Government (COG) site designed to house and protect key government and military personnel in the event of a catastrophic nuclear, chemical, or other devastating attack on the United States.
The complex has been described as an "underground Pentagon" due to its comprehensive emergency operations centers for the Army, Navy, Air Force, and Marine Corps. Situated within Raven Rock Mountain, the bunker represents one of the most extensive government survival measures undertaken during the Cold War period.