Question: What underground nuclear bunker near Blue Ridge Summit, Pennsylvania known as "underground Pentagon" became operational in 1966?
Sentence (from "Deep Underground Command Center"): The Deep Underground Command Center (DUCC) was a United States military installation that was proposed on January 31, 1962 , to be "a very deep underground center close to the Pentagon, perhaps 3,000-4,000 feet down, protected to withstand direct hits by high-yield weapons and endure about 30 days in a post-attack period" .
Relevant evidence: No