SAGE Air Defense

Vannevar Bush "General of Physics"
from Time 1944/04/03
SAGE in CHM - cu
SAGE artifact for museum
from MIT
The Air Force in 1954 began the SAGE (Semi-Automatic Ground Environment) project at MIT (Massachusetts Institute of Technology) where Vannevar Bush had created a large research organization in WWII for his OSRD (Office of Scientific Research and Development). Jay Forrester and George Valley at MIT's Lincoln Lab wrote a report in 1948 that described a plan to expand the air defense of the United States using the radar technology developed at MIT during World War II. As Cold War policies changed from containment to coercion after the Korean War and NSC/68, the military-industrial-university complex was mobilized to develop new weapons and strategies. The 1948 Lincoln Lab plan evolved by 1954 into a program that exceeded the Manhattan project in cost and scale. Four private corporations became contractors for a national defense system. IBM developed computer hardware, Burroughs developed communications, Western Electric designed and constructed the 23 concrete "Direction Center" buildings, and the Lincoln Lab (that became the MITRE Corporation in 1958) provided system integration.

By the time the system was fully deployed in 1963, according to MITRE, "the 24 SAGE Direction Centers and three SAGE Combat Centers were spread throughout the U.S. Each was linked by long-distance telephone lines to more than 100 interoperating air defense elements, requiring system integration on a scale previously unimagined. At the heart of each center was a new large-scale digital computer that had evolved from MIT's experimental Whirlwind computer of the 1950's. The largest real-time computer program of that time, it automated information flow, processed and presented data to 100 operator stations, and provided control information to the weapons systems. This processed information, including aircraft tracks and identification, was presented to operators on a cathode ray tube -- one of the first uses of this device to display computer-generated data." Each Center was built around a huge A/N FSQ-7 computer with 60,000 vacuum tubes requiring 3 megawatts of power and running the largest computer program written up to that time, with 500,000 lines of code. This program used an area in system memory called COMPOOL that could be shared by several subroutines. This would become one of the founding concepts for the COBOL computer language. The communications devices from Burroughs allowed each center to communicate with other centers, creating one of the first practical computer networks.

The Burroughs company also developed a backup system. According the the BUIC Fact Sheet, "Back Up Interceptor Control System (BUIC) is a semi-automatic backup to SAGE which provides for conduct of the air battle in the event that portions of SAGE become inoperative. Burroughs Corporation is providing the AN/GSA-51 Radar Course Directing Group that consists of a Burroughs D825 modular data processing system. It is in the modular data processor that the operational program is stored and executed. For the BUIC application, two computer modules, six memory modules and three input/output modules are utilized. Data exchange occurs simultaneously between any memory and any computer or input/output module. The modular nature of the equipment not only permits operation of the system when some modules are inoperative, but also permits convenient expansion to increase capability. The data processor can be readily expanded to up to four computers, 16 memories and 20 input/output modules with no obsolescence of hardware or software. Input/output modules for the BUIC system consist of message processors and controller-comparators. BUIC accepts radar information from long range radar sites via the message processors. The data is temporarily stored, formatted into computer words, and transferred to core memory via a controller-comparator. Controller-comparators handle data transfers between core memory and all devices except computers. A computer, operating on the data stored in core memory, performs all the computations necessary for generating appropriately formatted display data. The display data, stored in core memory, is transferred via a controller-comparator to the display fields of a drum, which in turn automatically presents this data to each display console 30 times each second. To accomplish all of this, the computer executes a succession of program segments called up from the drums. Display data available at each display console, which includes up to 12,288 symbols or vector segments, is selected by an operator by means of 15 category selectors. Radar data displayed includes current data together with up to seven history points to permit track initiation. Once the operator initiates a tracking action by means of a light pen on the display, the computing system automatically maintains the track by prediction and examination of incoming data for correlation. Height requests are automatically generated and transmitted based on track priority, or may be operator initiated. When it is established that defensive action is to be taken, the operator can call up weapons status information, which is being continually updated via card reader inputs. He can then call upon the computer for solutions to possible intercepts, the solutions being made to appear at the requesting display console. Once a weapon is assigned, the computer generates the necessary launch and guidance commands, and the track on the weapon is initiated automatically. The launch and guidance commands, stored momentarily in core memory, are accepted by the message processor, formatted, and transmitted over the appropriate communication lines. All the while, messages are being exchanged as required with adjacent air defense sectors."

According to Jim Ray, "SAGE was one of the engineering marvels of the century. In fact if it looked better, it might have been ranked with the Eiffel Tower, the Saturn Rocket or the Golden Gate Bridge for engineering accomplishment. It also pioneered some of the most of the important technology used to facilitate internet processing today: i.e., the modem, the mouse [light gun], multi-tasking, array processing, computer learning, fault detection, magnetic memory, and interactive computer graphics. Most important, it worked well enough for each center to coordinate about 100 operators , track 300 simultaneous flights, control numerous sorties against a maneuvering radar-jamming 'enemy', and coordinate 'friendly' NIKE and Bomarc defenses."

The last SAGE Direction Center was dismantled in 1983, but its influence on the development of computer technology was already significant. Lawrence Roberts came from the Lincoln Laboratory to work in 1965 at the Information Processing Techniques Office (IPTO) of the Advanced Research Projects Agency (ARPA) that had been established in 1958 after Sputnik. The director of IPTO in 1962 was J. C. R. Licklider, also from MIT and SAGE, who with Roberts would be key designers of the ARPANET that became a reality in 1969. Kenneth H. Olsen from MIT and SAGE founded the Digital Equipment Corportation (DEC) in 1957 and developed the PDP-1 computer in 1960 and the PDP-8 in 1968, called the first mini-computer because it was small like the mini-skirt.

SAGE in CHM - cu


Many thanks to Jim Ray and to the MITRE Corporation for permission to quote from their web sites cited in the Sources. This page was revised 3/31/03 by Schoenherr