Whirlwind and the Roots of Continental Air Defense

The first Soviet nuclear test in 1949 forced the newly-formed US Air Force to confront a serious lag in defensive technology. Among the resulting accelerated projects was one using a radical approach centered on the recently-invented digital computer as the core of a system that could combat massive attacks with continental reach. This paper examines the very early development of technology on MIT’s Whirlwind computer that eventually grew into the Semi-Automatic Ground Environment (SAGE). The topic is explored through the functional restoration of one computer program, David Israel’s 1951 “track-while-scan and intercept” program, which demonstrated for the first time the possibility of linking radar systems with emerging digital computers to track and intercept hostile aircraft in real time. From that first demonstration, we will see some of the key ideas in system architecture and user interaction that carried all the way through to deployment of the operational SAGE system.