Original plans called for twelve sites, but an interim agreement signed on May 26, 1972, after the Strategic Arms Limitations Talks I limited strategic missile defenses to 200 interceptors each and allowed each side to build only two missile defense sites, one protecting the national capital and one protecting an ICBM field. The Montana site, only 10 percent complete, was abandoned on May 27, 1972, and when Congress did not authorize the permitted deployment in Washington, DC, the North Dakota site became the only one of its kind ever fully constructed. Construction of the Stanley R. Mickelsen Safeguard Complex began on April 6, 1970; its Equipment Readiness Date was October 10, 1974; initial operating capability was reached by April 1, 1975; and full Safeguard operational capability was reached on October 1, 1975. Although a common misconception holds that it operated for only one day, the complex had Limited Combat Ready Status earlier in April 1975 and was operational from the Equipment Readiness date of October 1, 1974, until February 10, 1976, when the Senate followed the House of Representatives, which had voted on October 2, 1975, to deactivate it after full operational capacity was achieved on October 1, 1975. With construction and final closure activities, the site remained active from 1970 to 1977, the doors to the Missile Site Control Building were welded shut in 1979, and the Perimeter Acquisition Radar, turned over to the Air Force, still operates. Constructing and fielding the system required major personnel and material resources: as of June 1975, the site employed 513 defense contractor engineers and technicians, 109 civil service personnel, and 430 U.S. Army personnel, while weather ranged from 38 degrees Celsius to minus 40 degrees Celsius, with 60 days of load limits during construction, and the PAR and MSR used 714,000 cubic feet of concrete, over 27,500 tons of reinforcing steel, 2,273 miles of wire, 44 million pounds of rebar, 750 miles of conduit, 40 miles of piping, and 685 tons of duct material.