Happy’s Tech Talk #9: Radars, Missiles, and the World’s Costliest Computer

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Let’s have a little fun and walk back nearly 70 years into the history of electronics and computers. What was the world’s costliest computer and why? The answer is not today’s supercomputers1, nor computers built during World War II. Instead, it lies in a real-time air defense radar system built during the height of the Cold War of the 1950s that had left the U.S. extremely vulnerable to a Soviet bomber attack.2

Introduction to SAGE
This was the beginning of a North American strategic defense system, eventually known as the Semi-Automatic Ground Environment System (SAGE). It was conceived in 1954 by the scientists at MIT’s Lincoln Laboratory for the air defense of the U.S. and Canada. The idea was that a large network of radars would automatically detect a surprise bomber formation as it approached the U.S. mainland from any direction2 (Figure 1). By the time of its full deployment, there were 24 direction centers, three combat centers, and hundreds of radars2. These were built to analyze radar data and respond with appropriate actions by directing Air Force and Navy interceptor fighters, and Air Force, Army, and Navy guided missiles (Figure 2).

(I actually grew up in Alsea, Oregon not far from Camp Adair, a SAGE command center, where I once got to tour the blockhouse. This station was in operation until the late 1960s—the middle of my college years in Corvallis.)

Many of the missiles along the Canadian border (like the BOMARC) had nuclear-tipped warheads that could explode over Canada. Fortunately, they were never used, although one accidentally blew up in New Jersey and contaminated the area with plutonium3. These were the first supersonic missiles. By 1949, the rockets could reach altitudes of 100,000 to 150,000 feet and had the capability of flying at Mach 6.94. To be effective, the SAGE system would have to direct interceptors and missiles to their target until their own radar acquired the targets. Smaller missiles were coordinated for city defenses (Nike Ajax/Nike Zeuz) and used conventional warheads. Construction was completed in 1962.

SAGE Hardware
To get the project underway, it was decided to use the experimental technology of an MIT-built computer, an IBM-Whirlwind II, the most powerful of its time. Each direction center housed a dual-redundant AN/FSQ-7 computer Happy_June_Fig3_cap.jpgthat consisted of over 500,000 lines of code and executed over 25,000 instructions, by far the largest computer programs ever written at that time2. The computers and personnel were all housed in a windowless concrete blockhouse (Figures 3 and 4a). The all-tube computer had an impressive set of components and characteristics6:

  • 49,000 vacuum tubes
  • 13,000 gallium transistors
  • 175,000 diodes
  • 256 KB of ferrite magnetic core RAM (Figure 3d)
  • 12 10.7-inch, 2900 rpm magnetic drum memory of 256 KB (disc drive not invented yet)
  • Six IBM-728 tape drives to store the software
  • Weighing an impressive 250 tons
  • Consuming 3 million watts of power
  • Occupying 21,780 square feet

In addition, it was the first computer to be networked, to have a completely redundant hot backup computer on standby, and to use large 20-inch CRTs as operating consoles.

The SAGE System


The undertaking of this ambitious system was monumental. Every U.S. state and Canada became involved (Figure 1). For the first time, all the independent defense Happy_June_Fig4_cap.jpgelements were connected to central control systems by underground dedicated telephone lines as well as radar picket ships and “Texas Towers” at sea, and airborne early warning. Also monumental were the hundreds of new long-range radars and unmanned, automated “gap filler radars” constructed across the U.S. and Canada. Burroughs and Western Electric had the responsibility for these computers and connecting all these elements together.

The SAGE Computer
The SAGE computers (Figures 4b and 5) were constructed on three of the four floors of the CC and DC blockhouses. They were interfaced to 150 operating consoles (Figure 5) that were manned by Air Force personnel on a 24/7 basis, all operating at a blistering 75,000 instructions per second (equivalent to an Intel 386).7

While some functions of the system were automatic, it still took an operator to spot and identify an unidentified radar target and decide whether it was friend or foe. The automatic part came because all domestic and military aircraft had filed flight plans that the computer had stored on a magnetic drum and would match to real-time radar data. If the operator decided that the flying object was “foe,” the track was moved to a combat center and the weapons director for actions. If interceptor fighters were scrambled, the
computer would guide them to intercept this Identification Friend or Foe (IFF). If a missile was employed, the computer would automatically guide the missile closer so that its own radar could be employed. Then warnings would go out to all civil defense alerts.

Happy_June_Fig6_cap.jpgFigure 6 shows a close-up of the SAGE computer computing module. The entire module was hand soldered. Considering the 7,000 modules per computer, and two computers in each of the 27 installations, 378,000 modules had to be manufactured by IBM, not counting spares. But availability was 99.97%.7

The Operating System

The software was written by the RAND Corporation with the help of IBM and System Development Corp. (SDC). The 250,000 lines of code, at the peak, employed 20% of the world’s programmers. The one million words of code were written in assembly language and JOVIEL. Forty-four manuals of schematics and specifications, including S/W coding, are available from IBM8.

The Final Outcome
By 1983, the system was finally shut down as ICBMs made it obsolete. Over the horizon, radars like the Distant Early Warning Line (DEW Line) and orbiting satellites were replacing it. It was not completely dismantled as many of the radars were upgraded and a newer SAGEII computer from Hughes was available to use the software; it was turned over to the FAA for domestic flight control.

The success of the system came at an enormous cost. While neither IBM nor the government have ever released production costs on the secretive (and now decommissioned) project, civilian estimates put the total
development cost at $8–$12 billion ($65–$97 billion when adjusted for inflation). This would be three times the cost of the Manhattan Project.

While source opinions vary on the effectiveness of this project, John F. Jacobs, associate head of Lincoln’s Division 6, stated:

“One of the outstanding things… was the esprit de corps—the spirit that pervaded the operation. Everyone had a sense of purpose—a sense of doing something important. People felt the pressure and had the desire to solve the air defense problem, although there was often disagreement as to how to achieve that end. Energy was directed more toward solving individual problems, such as making a workable high-speed memory or a useable data link, than it was toward solving the problem of the value of the finished product. It was an engineer’s dream.” 9

What I found was that the system pioneered many firsts:

  • Real-time computer architectures
  • Core memory
  • Magnetic drum memory
  • Networking of sensors, computers, autonomous elements, and humans
  • Simple CRT operator interfaces—light pen

The irony of the SAGE computer is that in its last few years of operations, replacement vacuum tubes had to be purchased from the Soviet Union, as they were no longer manufactured in the West.  PCB007


  1. The Chinese Sunway TaihuLight is the world’s fastest supercomputer. It became active in 2016 at a cost of $273 million. Wikipedia.com.
  2. History of SAGE: Semi-Automatic Ground Environment, Lincoln Laboratory, MIT.
  3. “Old Missile Site at McGuire is Still Tainted, Kean Says,” New York Times, July 10, 1985.
  4. “The United States developed the first hypersonic missile in 1949,” We Are the Mighty, April 13, 2022.
  5. Locklin on science: The largest computer ever built, March 28, 2013.
  6. “The Computer Museum Member’s First Field Trip to Northbay AN/FSQ7 SAGE Site and to the Canadian National Museum of Science and Technology,” by Gordon Bell, Oct. 10, 1982.
  7. The SAGE System, Computer History Museum.
  8. IBM SAGE specs, bitsavers.trailing-edge.com.
  9. “The SAGE Air Defense System, A Personal History,” by John F. Jacobs, The MITRE Corporation.

Happy Holden has worked in printed circuit technology since 1970 with Hewlett-Packard, NanYa Westwood, Merix, Foxconn, and Gentex. He is currently a contributing technical editor with I-Connect007, and the author of Automation and Advanced Procedures in PCB Fabrication, and 24 Essential Skills for Engineers.

This column originally appeared in the June 2022 issue of PCB007 Magazine.


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