AN/FSQ-7 Combat Direction Central

AN/FSQ-7 Combat Direction Central
Military command, control and coordination system
The AN/FSQ-7 included a Maintenance Intercom System
(phone on end of cabinet).
Country United States
Command 1958-1968: Air Defense Command
1968-1979: Aerospace Defense Command
Direction center
AL: Gunter Annex (DC-09)
AZ: Luke Air Force Base (DC-21)[1]
CA: Norton Air Force Base (DC-17)
ME: Bangor Air National Guard Base (DC-15)
MI: Custer Air Force Station (DC-06)
MI: K.I. Sawyer AFB (DC-14)
MN: Duluth Air National Guard Base (DC-10)
MO: Richards-Gebaur Air Force Base (DC-08)
MT: Malmstrom Air Force Base (DC-20)
ME: Topsham Air Force Station (BaADS)(DC-05)
ND: Grand Forks Air Force Base (DC-11)
ND: Minot Air Force Base (DC-19)
NJ: McGuire Air Force Base (DC-01)
NV: Stead AFB (DC-16)
NY: Hancock Field (Syracuse AFS) (DC-03)
NY: Stewart Air Force Base (DC-02)
ON:CFB North Bay, Ontario (DC-31)
OR: Adair Air Force Station (DC-13)
VA: Fort Lee Air Force Station (DC-04)
WA: McChord Air Force Base (DC-12)
WI: Truax Field (DC-07)
This list is incomplete; you can help by expanding it.
Part of Semi-Automatic Ground Environment
Area 21,000 sq ft (1,950 m2) [2]:77 floor space, both
USAF Cambridge Research Laboratory[4]
MIT Lincoln Laboratory[5]
IBM Military Products Division
(renamed IBM Federal Systems in 1959)

The AN/FSQ-7 Combat Direction Central (colloq. Q7) was a computerized command and control system for Cold War ground-controlled interception used in the USAF Semi-Automatic Ground Environment (SAGE) air defense network.[5] The largest computer system ever built, each of the 24 installed machines[7]:9 weighed 250 tons and had two computers.[8] The AN/FSQ-7 used a total of 60,000 vacuum tubes[8] (49,000 in the computers)[7]:9 and up to 3 megawatts of electricity, performing about 75,000 instructions per second for networking regional radars.

The installations were configured as duplex systems, using a pair of AN/FSQ-7 computers to provide fault tolerance. One was active at any time, the other on standby. The standby system copied data from the active system to minimize switchover time if needed. A scheduled switchover took place every day.[2]:179–181

The AN/FSQ-7 calculated one or more[5] predicted interception points[3] for assigning manned aircraft or CIM-10 Bomarc missiles to intercept an intruder using the Automatic Target and Battery Evaluation (ATABE) algorithm.[9] Also used in the Nike AN/FSG-1 system, ATABE automated the Whiz Wheel (Felsenthal CPU-73 A/P Air Navigation Attack Computer)[10] method used in manual command post operations.[11]

The Q7 fire button launched the Bomarc,[12] and an additional Q7 algorithm automatically directed the missile during climb and cruise to the beginning of its supersonic dive on the target when guidance transferred to the missile seeker system for the homing dive.[3]:30–3 Later improvements allowed transmission of Q7 guidance to autopilots of manned fighters for vectoring to targets[13] via the SAGE Ground to Air Data Link Subsystem (cf. bomber vectoring to a Bomb Release Point in 1965-73 Vietnam via vacuum-tube analog computers.)


The first US radar network used voice reporting to the 1939 Twin Lights Station in New Jersey, and the post-World War II experimental Cape Cod System used a Whirlwind I computer at Cambridge to network long-range and several short-range radars. The key Whirlwind modification for radar netting was the development of magnetic core memory that vastly improved reliability, operating speed (×2), and input speed (×4) over the original Williams tube memory of the Whirlwind I. The AN/FSQ-7 (“AN/FSQ” derives from Army-Navy / Fixed Special eQuipment)[14] was based on the larger and faster Whirlwind II design, which was not completed[5] and was too much for MIT's resources (Lincoln Laboratory Division 6 still participated in AN/FSQ-7 development).[15] Similar to the Q7, the smaller AN/FSQ-8 Combat Control Central was produced without an Automatic Initiation Area Discriminator and other equipment.[16]:151

The experimental SAGE subsector, located in Lexington, Mass., was completed in 1955, equipped with a prototype AN/FSQ-7 known as XD-1[17] in Building F. The third evaluation run with the XD-1 was in August[15] and the prototype was complete in October 1955 except for displays.[18] By 1959, the 2000th simulated BOMARC intercept had been completed by the Q7, while the Cape Canaveral BOMARC 624-XY1's intercept of a target drone in August 1958 used the Kingston, New York, Q7[3]:57 1500 miles away.[19] DC-1 at McGuire AFB was the first operational site of the AN/FSQ-7[5]:11:10 with consoles scheduled for delivery Aug-Oct 1956.[20] Groundbreaking at McChord Air Force Base was in 1957[21] where the "electronic brain" began arriving in November 1958.[22]

The SAGE/Missile Master test program conducted large-scale field testing of the ATABE mathematical model using radar tracks of actual Strategic Air Command and Air Defense Command aircraft conducting mock penetrations into defense sectors[9] (cf. Operation Skyshield). The vacuum-tube SAGE network was completed (and obsolete) in 1963, and a system ergonomic test at Luke Air Force Base in 1964. According to Harold Sackman, it "showed conclusively that the wrong timing of human and technical operations was leading to frequent truncation of the flight path tracking system."[7]:9 Backup Interceptor Control Systems (BUIC) were used to replace the AN/FSQ-7s:[7]:10 two remained at SAGE sites until 1983[7]:9 including McChord AFB,[23] and the Q7 at Luke AFB was demolished in February 1984.[24]

The SABRE airline reservation system used AN/FSQ-7 technology.[25] Q7 components were used in numerous films TV series and TV series needing futuristic looking computers, despite the fact they were built in the 1950s. Q7 components were used in The Time Tunnel, The Towering Inferno, Logan's Run, WarGames and Independence Day amongst many others.[26] The Computer History Museum displays several AN/FSQ-7 components.


MIT selected IBM as the prime contractor for equipment construction.[27] The Central Computer System of the AN/FSQ-7 had two computers for redundancy each with Arithmetic, Core Memory, Instruction Control, Maintenance Control, Selection & IO Control, and Program elements.[28] The Q7 had input/output devices such as:

Punched card data was transferred to and from the core memory as binary images. Only the right 64 columns were transferred, with each row containing two 32-bit words. (The left columns could be punched using a special instruction.) Data was transferred to the line printer as a card image as well.[16]:125

Core memory element

The FSQ-7 and -8 used core memory with 32-bit words plus a parity bit, operating at a 6-microsecond cycle time. Both machines had two banks of memory, memory 1 and memory 2. On the FSQ 7 memory 1 had 65,536 words and memory 2 had 4096 words. On the FSQ-8, each bank had 4096 words.

For data storage, each word was divided into two halves, each half was a 15-bit number with a sign bit. Arithmetic operations were performed on both halves simultaneously. Each number was treated as a fraction between -1 and 1. This restriction is placed on data primarily so that the multiplication of two numbers will always result in a product smaller than either of the numbers, thus positively avoiding overflow. Properly scaling calculations was the responsibility of the programmer.

Instructions used the right half word plus the left sign bit to form addresses, yielding a 17-bit address space. The remainder of the left half word specified the operation. The first three bits after the sign specified an index register. The following bits specified an instruction class, class variation and instruction-dependent auxiliary information. Addresses were written in octal notation, with the two sign bits forming a prefix, so 2.07777 would be the highest word in memory 2.

Arithmetic registers were provided for both halves of the data word and included an accumulator, an A register that held the data value retrieved from memory, and a B register that held the least significant bits of a multiplication, the magnitude of a division, as well as shifted bits. There was also a program counter, four index registers, and a 16-bit real time clock register which was incremented 32 times a second.[16]:27 Trigonometric sine and cosine functions used 1.4 degree precision (256 values) via look-up tables.[16]:67

External video
"On Guard! The Story of SAGE"
AN/FSQ-7 used for Bomarc launch
"In Your Defense" (Col. John Morton, narrator)

See also


  1. Murphy, Michael F. "AN/FSQ7 SAGE Computer: Luke AFB" (personal notes). Retrieved 2012-04-02. Luke center was unique in the fact that it was the programming center for all other sage sites. This only meant that our computers…had more core memory, 32K total
  2. 1 2 3 Bernd Ulmann (August 2014). AN/FSQ-7: the computer that shaped the Cold War. de Gruyter Oldenbourg. ISBN 978-3-486-85670-5.
  3. 1 2 3 4 The SAGE/BOMARC Air Defense Weapons System (Fact Sheet) (Report). IBM Military Products Division. Retrieved 2012-04-02. On August 7, 1958, the IBM/SAGE computer at Kingston [the IBM facility] undertook the first remote-controlled intercept of a drone target by a BOMARC missile. The BOMARC was fired from Cape Canaveral and the intercept was made at sea.:15
  4. "AN/FSQ-7 "Whirlwind II" & AN/FSP-8 Intercept Computer". Retrieved 2012-04-02.
  5. 1 2 3 4 5 In Your Defense (digitized movie). Western Electric. Retrieved 2012-04-03. The System Development Corporation…in the design of massive computer programs … Burroughs…electronic equipment … Western Electric…assist the Air Force in coordinating and managing the entire effort…and design of buildings. …SAGE project office…Air Material Command NOTE: The film identifies "Direction Center" versus "Data Center".minute 5:15
  6. "IBM Archives: 1959". Retrieved 2013-12-24.
  7. 1 2 3 4 5 Hellige, Hans Dieter (Februar [sic] 1993). Actors, Visions and Developments in the History of Computer Communications (PDF) (Report). "Work and Technology" Research Centre. Retrieved 2012-04-02. Check date values in: |date= (help)
  8. 1 2 Granelia, Mark. "IBM-SAGE-Computer". Retrieved 2012-04-02.
  9. 1 2 A Survey and Summary of Mathematical and Simulation Models as Applied to Weapon System Evaluation (Report). Aeronautical Systems Division, USAF. December 1961. Retrieved 2011-09-13. Future experiments and/or tests: Data from the Phase II and Phase III NORAD SAGE/ Missile Master test program is to be used to validate the mathematical model. These are large-scale system tests employing SAC and ADC aircraft. The field test program is the responsibility of the NORAD Joint Test Force stationed at Stewart Air Force Base. (cites Miller 1961)
  10. "Whiz Wheel". Retrieved 2013-12-24.
  11. "sources". Retrieved 2013-12-24.
  12. 1 2 DeWerth, John P. …Sage Memories (personal notes) (Report). Retrieved 2012-04-03.
  13. compiled by Johnson, Mildred W (31 December 1980) [February 1973 original by Cornett, Lloyd H. Jr]. A Handbook of Aerospace Defense Organization 1946 - 1980 (PDF). Peterson Air Force Base: Office of History, Aerospace Defense Center. p. . Retrieved 2012-03-26.
  14. Dyson, George (April 1997). Darwin Among the Machines: The Evolution of Global Intelligence (1 ed.). Basic Books. p. 179. ISBN 0-7382-0030-1.
  15. 1 2 Division 6 Staff. Biweekly Report for 27 May 1955 (Memorandum) (Report). MIT Lincoln Laboratory.
  16. 1 2 3 4 5 Theory of Programming for AN/FSQ-7 combat direction central and AN/FSQ-8 combat control central (PDF) (Report). IBM Military Products Divistion. April 1, 1959. Retrieved 2012-04-02.
  17. Introduction to AN/FSQ-7 Combat Direction Central and AN/FSQ-8 Combat Control Central ( transcription) (Report). Kingston, New York: International Business Machines Corporation. Retrieved 2012-04-02.
  19. "CBC Digital Archives". Retrieved 2013-12-24.
  20. Division 6 Staff. Biweekly Report for 4 May 1956 (Memorandum) (Report). MIT Lincoln Laboratory.
  21. John Pike. "Semi-Automatic Ground Environment - United States Nuclear Forces". Retrieved 2013-12-24.
  22. "Electronic Brain Slated To Arrive". Tri-City Herald. Google News Archive. November 3, 1958. Retrieved 2012-04-02.
  23. 1 2 "SAGE A/N FSQ-7". Retrieved 2013-12-24.
  24. "SAGE- Phoenix Air Defense Sector & 4629 Support Squadron". Retrieved 2013-12-24.
  25. "Computer History". Plyojump. Retrieved 2013-12-24.
  26. Loewen, Mike (March 13, 2012). "The AN/FSQ-7 on TV and in the Movies". Retrieved 2012-04-02.
  27. Bash, Charles J. and others (1986) IBM's Early Computers, MIT, pp.240-248
  28. Theory of Operation AN/FSQ-7(XD-1, XD-2) Combat Direction Central: Central Computer System (Preliminary Manual) (Report). Poughkeepsie, New York: International Business Machines Company. September 1955. Retrieved 2012-04-02. introduction of the air defense [software] program … from the Drum System when available and needed. … For more information on the subject of programming, refer to PH 45-00002.:57 (one of various SAGE documents at
  29. 1 2
  30. Karculias, Pete. "description of 1967-9 SAGE photographs". SAGE A/N FSQ-7 [webpage]. Southwest Museum of Engineering, Communications and Computation. Retrieved 2012-04-02.
  31. "Semi-Automatic Ground Environment (SAGE)". MITRE corporation.
Preceded by
World's most powerful computer
1958 - 1959
Succeeded by
IBM 7090
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