Task: Explanation
Input (English): The Raven Rock Mountain Complex (RRMC) is an American military installation with an underground nuclear bunker near Blue Ridge Summit, Pennsylvania, at Raven Rock Mountain that has been called an "underground Pentagon." The bunker has emergency operations centers for the United States Army, Navy, and Air Force. Along with Mount Weather Emergency Operations Center in Virginia and the Cheyenne Mountain Complex in Colorado, it formed the core bunker complexes for the US Continuity of Government plan during the Cold War to survive a nuclear attack. Question: What underground nuclear bunker near Blue Ridge Summit, Pennsylvania known as "underground Pentagon" became operational in 1966? Answer: Raven Rock Mountain Complex
Output (English): The Raven Rock Mountain Complex RRMC is an American military installation with an underground nuclear bunker near Blue Ridge Summit, Pennsylvania, at Raven Rock Mountain that has been called an underground Pentagon.