The Second World War demonstrated the devastation that could be caused by even conventional bombing…and was capped by the nuclear destruction of Hiroshima and Nagasaki. With the intensification of the Cold War and the first Soviet atomic bomb test…and the Communist aggressiveness demonstrated by the outbreak of war in Korea…air defense of the United States became an issue of very high priority.
During World War II, the British had been successful with their innovative network of radar stations linked to command centers at which the positions of friendly and enemy aircraft were plotted continuously and orders issued to fighter squadrons and antiaircraft gun sites. In the postwar era, though, the increased speeds of combat aircraft, combined with the utter devastation that could result from a single failed intercept–one plane, one bomb, one city–drove the view that something better than manual plotting would be required.
Although digital computers were still very much in their infancy in 1953, the solution to the air defense problem chosen in that year was a computer-based system to be known as SAGE…the Semi-Automatic Ground Environment. Real-time information from multiple radar sites flowed in digital form to the computers at the SAGE Direction Centers. The computers tracked the targets, friendly, unknown, and enemy, and displayed them on dozens of video displays at each Center. Battle-management personnel at these displays made the determination of which enemy targets should be engaged with what priority, and what friendly aircraft should engage them, and the computers then calculated the optimum intercept courses. For certain fighter aircraft types, the interception commands could be relayed directly via datalink, obviating the necessity for voice communication. SAGE Direction Centers also had control over high-speed BOMARC antiaircraft missiles…these carried small nuclear weapons intended to ensure that a near miss would not allow enemy bombers to escape.
At the heart of each Direction Center was a pair of computers, AN/FSQ-7, duplexed for reliability. Each pair contained fifty thousand vacuum tubes, covered almost an acre of floor space, and consumed about 3 megawatts of power. (Some sources cite the 50,000-tube number as being for each computer of the pair–either way, it’s a LOT of vacuum tubes.) Here’s a fairly well-done recent article about the SAGE project. Note, however, the author’s comment about “thousands of people all over North America constantly scanning their radar screens for Soviet attacks, all hankering for an opportunity to launch a radio-controlled nuke.” I wonder: does this guy really believe that the airmen at the SAGE scopes were really looking forward to a nuclear war, or did he just think that’s the sort of thing that would play well with his editors and his audience?
Developing the hardware required for SAGE was a challenge; developing the software even more so. IBM’s Tom Watson Jr explained the issue: ”In those days computing was typically done in what was called batch mode. This meant that you would collect your data first, feed it into the machine second, then sit back for a little while until the answer came out. You could think of the batch processor as a high diver at a circus–each performance involves a lengthy drum roll in preparation, a very fast dive, and then a splash. But the SAGE system was supposed to keep track of a large air defense picture that was changing every instant. That meant it had to take a constant stream of new radar information and digest it continually in what is called “real time.” So a SAGE computer was more like a juggler who has to keep a half dozen balls in the air, constantly throwing aside old balls as his assistant toss him new ones from every direction.”
Each SAGE computer had to accept continuous streams of data sent from the radar sites over leased telephone lines (this was the first large-scale example of computer networking) as well as flight plan data from the airlines and the FAA, perform tracking and intercept calculations, manage the display of information on dozens of screens, and–when required–transmit data link commands to properly-equipped interceptors and direct the flight of one or more BOMARC missiles. All of this had to be accomplished with a computer rated at only 75,000 instructions per second, far slower than whatever device you are using to read this post.
The initial operational deployments of SAGE were in 1958, and the full nationwide system was in place by 1962. This was a vast project, requiring not only the production and development of the computer systems and interfaces, but also massive construction efforts. Total cost was somewhere around $8 billion, which translates into roughly $63B in 2013 dollars. SAGE ran until 1984, when it was replaced with more modern technology.
Some have asserted that SAGE became obsolete when the Soviets launched Sputnik in October 1958, but I think this is a considerable overstatement. Development and deployment of Soviet intercontinental missiles could not take place instantaneously, and certainly at the time of the Cuban Missile Crisis, in 1962, manned bombers were still an important factor in the balance of forces calculations of the two powers. (Also, of course, SAGE technology was–at least at the conceptual level if not the hardware and code level–directly relevant to the development of missile warning systems.)
Whether or not SAGE was a wise investment from a national defense standpoint, it certainly had a major technological impact. At the hardware level, it was the first major system to use magnetic core memory. Experience gained in on-line systems development led directly to the use of computers for airline reservations systems and air traffic control–indeed, one of the SAGE Direction Centers was actually used for ATC purposes for a while. SAGE was the first large-scale system to use visual displays, and the use of the light gun to select objects on these screens was the predecessor of the mouse. SAGE pioneered to development of data communications, which would lead eventually to the Internet.
Here’s another recent article on SAGE. It’s mostly political ax-grinding, and I don’t think it’s very accurate; I’m linking it mainly because the discussion thread includes comments from people who actually worked on the system. (Another recent article, the link to which I have lost, referred to SAGE as being motivated by the “Red Scare,” as if it had been irrational to be concerned about nuclear weapons in the hands of Josef Stalin and his successors.)
While researching this post, I encountered several interesting items of SAGE lore:
–Early in the operational deployment of SAGE, someone (of course!) figured out how to use the system to create an image of a pin-up girl on the display screen. Here she is. (A comment here notes that displaying pictures of unclothed young women is somewhat unrelated to national defense..unless one takes a very long view.)
–Each SAGE Direction Center was connected, via redundant land lines, to the BOMARC missile sites over which it had control. If one line failed, a black box at the missile site would switch the listening watch to the other line. An analyst discovered that if this second line also failed, the equipment would just keep listening to the noise on the bad line. He did a little math and showed that in this situation, random noise would generate something that looked like a FIRE command, probably within two minutes…receipt of this command would cause the missile to erect to a firing position and begin its launch sequence.
This actually happened, only two weeks after the analyst wrote his report, scaring the hell out of the personnel at a BOMARC site near Washington DC. Apparently there was actually not much danger of an actual inadvertent launch: a whole sequence of acceptable guidance commands would have to have been received during a short window, and the analysis showed this to be very improbable. Still, very spooky for all involved, I imagine.
–SAGE makes an appearance in John Updike’s 2007 novel Villages, which I have not yet read.