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Raven Rock (Site R)
The "underground Pentagon" on the Pennsylvania line
The Raven Rock Mountain Complex, known as Site R, is a hardened underground military command center dug into a mountain in southern Pennsylvania near the Maryland border, not far from Camp David. Built in the 1950s, it is sometimes called the "underground Pentagon" — an alternate command facility intended to keep military leadership functioning during a national emergency. It remains an active, restricted installation whose interior details are classified.