Desert bighorn sheep establish two desert areas in southwestern Arizona to help preserve the desert bighorn sheep: Cabeza Prieta National Wildlife Refuge and the Kofa National Wildlife Refuge. In 1941, the San Andres National Wildlife Refuge in New Mexico was added. Desert bighorn sheep populations have trended upward since the 1960s when their population was estimated at 6,700-8,100. The upward trend was caused by conservation measures, including habitat preservation. In 1980, desert bighorn sheep populations were estimated at 8,415-9,040. A state-by-state survey was conducted a few years later and estimated the overall US desert bighorn sheep population at 15,980. The 1993 estimate of
US signals intelligence in the Cold War Desert Shield Desert Storm. COMBAT APPLE aircraft began to gather SIGINT overland, over the Ho Chi Minh trail and Laos. They went without fighter cover, and in the threat envelope of antiaircraft guns and missiles. When the US detected the antiaircraft weapons, it quickly attacked them, and the North Vietnamese quit trying to shoot down the COMBAT APPLEs. Several other ELINT versions of the RC-135 flew out of Kadena for specialized ELINT collection, with some aircraft flying missions of 24 hours and more while still based at Offutt AFB, Nebraska, in the US. Flying from Kadena, the RC-135C model, called