Cape Cod SAGE Prototype (part 2)

Testing the Cape Cod System

Formal trials of the Cape Cod System began in October 1953, with flight tests two afternoons a week. The tests continued until June 15, 1954, and analysis of the initial test results was highly favorable. Track initiation, tracking, and identification were accomplished successfully.

Over the next few months, the Cape Cod System was expanded to include long-range AN/FPS-3 radars at Brunswick, Maine, and Montauk Point on the eastern tip of Long Island, New York. Additional gapfillers were built and integrated, completing the expanded radar network in the summer of 1954.

Jet interceptors were assigned to support the experiments: 12 Air Force F-89Cs at Hanscom Field and a group of Navy F-3Ds at South Weymouth, Massachusetts. Later, an operational Air Defense Command (ADC) squadron of F-86Ds based at the Suffolk County Airfield on Long Island was integrated into the Cape Cod System, and the Air Force arranged for Strategic Air Command training flights in the Cape Cod area so the Cape Cod System could be used for large-scale air defense exercises against Strategic Air Command B-47 jet bombers.

The time had come to test the Cape Cod System with a live interception. In a joint experiment with the MIT Instrumentation Laboratory (now the Charles Stark Draper Laboratory), a B-26 aircraft equipped with an autopilot was connected to the Whirlwind computer, and interceptor vectoring commands were transmitted automatically over the data link to the autopilot. The interception went as planned. The pilot soon sighted the target aircraft and let the autopilot complete a successful interception. Another important first had been accomplished.

Prototype intercept monitor roomPrototype intercept monitor room in the SAGE direction center in MIT's Barta building. Picture used with the permission of the MITRE Corporation (copyright © The MITRE Corporation. All rights reserved).

The year 1955 was a watershed for the SAGE effort, with the focus of the program changing from installation and component testing to integrated system testing. The style of the program changed as well because the Air Force had given SAGE a precisely defined set of specifications.

On March 7, Air Defense Command (ADC) headquarters issued the Operational Plan for SAGE, prepared jointly by ADC and Lincoln Laboratory. The 300 pages provided "an overall understanding of the system, the concept of its operation, and the method by which it will be integrated into the Air Defense Command." The Operational Plan specified the equipment and personnel, the operational interactions between them, and their relationship within ADC. From that time on, work on SAGE had one overriding goal—to meet the specifications in the Operational Plan.

A new series of Cape Cod tests began in August 1955. Operator tasks in the direction center were changed so that they more closely resembled an actual SAGE subsector. Weapons-direction procedures were refined and training facilities were improved.

The basic concepts of automated air defense were demonstrated,
and the tests showed that an automated air defense system
could detect and intercept incoming aircraft.

The computer was able to process data from all 13 radars, and it could control manned interceptors and guide antiaircraft operation centers. The system had a capacity of 48 tracks that could be viewed in track situation displays, which geographically showed Air Defense Identification Zone lines and antiaircraft circles.  Each console also had a 5-inch CRT for digital information display. Audible alert signals were used, with a different signal for each symbol on a situation display.

A major goal of the Cape Cod tests was to gather data that could be used for simulating interceptions. Simulations in the early series were based entirely on live tests, but the data gathered in 1955 made it possible to combine live clutter data and live flight data to create new combat situations. The ability to use test data to simulate new conditions was a ground-breaking innovation in computer programming. Outside Lincoln Laboratory, the simulations occasioned doubt and controversy, but the results of the simulations established their accuracy and realism, and they were ultimately accepted as a practical alternative and a valid part of test and training procedures.

Beginning in November 1955, Lincoln Laboratory initiated a set of system exercises with live aircraft, known as the System Operation Test (SOT) series. These tests were conducted in a series of missions of increasing complexity.

The Series I SOT comprised eight tests, flown between November 15, 1955, and January 31, 1956. During each test, B-29 strike aircraft made radial attacks against Boston, which was defended by aircraft from the Hanscom and South Weymouth air bases. A total of 50 aircraft were sent against the system. Against these aircraft, 62 interceptors were sent to defend the airspace, 24 of which successfully intercepted the strikes.

The Series II SOT, flown between February 14 and April 25, 1956, was still more dramatic and realistic. As many as 32 high-speed B-47 aircraft flown by the Strategic Air Command attacked targets in Boston as well as Martha's Vineyard, Massachusetts, and Portsmouth, New Hampshire. Raids included multiple aircraft performing complex maneuvers: flying less than 1000 ft apart, making turns, and crossing, splitting, or joining tracks.

In the Series III SOT, carried out between July 6 and November 7, 1956, Boston was given a defense force of 16 interceptors from four air bases: Otis, Westover, Hanscom, and South Weymouth. Waves of B-47s attacked in groups of 12 to 16 aircraft, with the aircraft closely spaced and performing numerous crossing maneuvers.

The final series of Cape Cod System tests, carried out in 1957, focused on the development of new tracking techniques and new interception logic, and they produced significant results. The tests showed that, as long as the intercept-direction capacity was not exceeded, the Cape Cod System was capable of guiding interceptors sufficiently to achieve an interception rate of almost 100%.

The Cape Cod System was a great success for Lincoln Laboratory. The basic concepts of automated air defense were demonstrated, and the tests showed that an automated air defense system could detect and intercept incoming aircraft. 

Success in the Cape Cod program, however, was not sufficient. The Operational Plan for SAGE called for a fully functional prototype, and the Cape Cod System was only a simplified model, with the most basic tracking and intercept-direction functions.

The Experimental SAGE Subsector

The Experimental SAGE Subsector (ESS) was essentially an expansion of the Cape Cod System. But, unlike the Cape Cod System, ESS was a fully operational prototype.

The emphasis during the ESS phase was on evaluation of the AN/FSQ-7(XD-1) computer before IBM began production of the AN/FSQ-7. ESS included most of the Cape Cod System sites, as well as some new ones, and it emulated the performance of an operational subsector. Radar data, aircraft flight plans, and meteorological information were transmitted automatically to the computer. The system was required to have overlapping radars, automatic crosstelling, height finding, a command post, and weather and weapons status totes. Radar coverage of the ESS represented a scaled SAGE subsector, although the boundaries actually overlapped the future McGuire, Stewart, and Brunswick subsectors.

Researchers at MIT's Barta building perform strobe trackingResearchers at MIT's Barta building perform strobe tracking on a manual plotting board for the Experimental SAGE Sector (ESS). Picture used with the permission of the MITRE Corporation (copyright © The MITRE Corporation. All rights reserved).

The ESS direction center was located in Lincoln Laboratory's Building F, completed in 1955, and all ESS sites were connected to the AN/FSQ-7(XD-1). The computer occupied the first floor, the direction center was on the second floor, and the power equipment was in the basement.

Four-story SAGE direction centerAbove is the typical four-story SAGE direction center. The direction center was prototyped as part of the Cape Cod System in Building F at Lincoln Laboratory. Below is a schematic of the four stories (click on figure for a larger view). Schematic is used with the permission of the MITRE Corporation (copyright © The MITRE Corporation. All rights reserved).

The functionality needed for the direction center was defined as a set of specifications that were then coded as part of the direction center active (DCA) computer program. The DCA program was written in four successive packages, each of which performed a specific group of air defense functions. It eventually contained more than half a million lines of code and in excess of 25,000 instructions.




Schematic of floor plan

The conclusion of the Cape Cod System and Experimental SAGE Subsector prototyping activities signaled the end of an era for Lincoln Laboratory. The Laboratory had been founded as an institution for research and development, but the focus of its work was changing to operational testing and production. Both within Lincoln Laboratory and at MIT, concern was growing about the future of the program. Was it within Lincoln Laboratory's charter to produce an operational system? Or should Lincoln Laboratory, as a part of a great technical university, restrict its efforts to research and development?  Within a year, these questions would break Lincoln Laboratory apart, and the Laboratory would transition SAGE to other organizations for implementation and move on to tackle other problems involving technology in the interest of national security.

An Air Surveillance Officer checks tracker initiator consoles at which operators use light guns to pinpoint tracks. Picture used with the permission of the MITRE Corporation (copyright © The MITRE Corporation. All rights reserved).

Back to part 1: Cape Cod SAGE Prototype

Adapted from E.C. Freeman, ed., Technology in the National Interest, Lexington, Mass.: MIT Lincoln Laboratory, 1995.

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