The Deep Underground Command Center (DUCC) proposed by January 31, 1962, was to be excavated "3,000-4,000 feet down" with ~ "located underground between the Mall and River entrances of the Pentagon" which are tbd feet above the mean Potomac waterline. Based on SAC's Deep Underground Support Center planned near the Cheyenne Mountain nuclear bunker, the DUCC plan was recommended to President Kennedy for fiscal year 1965 funding shortly before his assassination, but the underground DUCC, SAC's DUSC, and NORAD's SCCs were never built. (The 1953 Site R was "hardened further to about 140 psi blast resistance by 1963", NORAD's Canadian bunker was completed in 1963, and NORAD's COC & SDC in the Colorado bunker became operational in 1966.)