Task: Explanation
Input (English): 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" . The DUCC would have been built as "an austere 50-man … or an expanded 300-man version (with the former built to permit expansion into the latter, if desired)" . It was designed to withstand multiple direct hits of 200 to 300 Megaton weapons bursting at the surface or 100 MT weapons penetrating to depths of 70-100 feet. Based on Strategic Air Command's Deep Underground "Support" Center (DUSC) planned near the Cheyenne Mountain nuclear bunker , the DUCC plan was recommended to President John F. Kennedy for fiscal year 1965 funding shortly before his assassination , but the underground DUCC, SAC's DUSC, and NORAD's Super Combat Centers were never built. Other contemporary underground installations did see upgrades, such as the 1953 Site R which was "hardened further to about 140 psi blast resistance by 1963" , or completion, such as the NORAD's Canadian bunker in 1963, and NORAD's Combat Operations Center & Space Defense Center in the Cheyenne Mountain bunker became operational in 1966. 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):  Other contemporary underground installations did see upgrades, such as the 1953 Site R which was hardened further to about 140 psi blast resistance by 1963 , or completion, such as the NORADs Canadian bunker in 1963, and NORADs Combat Operations Center  Space Defense Center in the Cheyenne Mountain bunker became operational in 1966.