By 1958, ensuring adequate warning of attack had become accepted as the paramount problem in air defense. This report concludes that the warning system should and can be augmented to provide (1) a high-quality, all-altitude surveillance perimeter several hundred miles deep, (2) an improved ground-based identification system, and (3) means for intercepting all unknown aircraft that penetrate such a perimeter inbound toward the United States.
Attaway, L. D., Programmed Warning of U.S.-Based SAC Against Air-Breathing Threats: Problems and Suggested Solutions. Santa Monica, CA: RAND Corporation, 1958. https://www.rand.org/pubs/research_memoranda/RM2236.html.
Attaway, L. D., Programmed Warning of U.S.-Based SAC Against Air-Breathing Threats: Problems and Suggested Solutions, Santa Monica, Calif.: RAND Corporation, RM-2236, 1958. As of October 27, 2021: https://www.rand.org/pubs/research_memoranda/RM2236.html