|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).
|Command||1958-1968: Air Defense Command|
1968-1979: Aerospace Defense Command
|AL: Gunter Annex (DC-09)|
AZ: Luke Air Force Base (DC-21)
CA: Beale Air Force Base (DC-18)
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 AFB (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)
|Part of||Semi-Automatic Ground Environment|
|Area||21,000 sq ft (1,950 m2) :77— floor space, both|
|USAF Cambridge Research Laboratory|
MIT Lincoln Laboratory
IBM Military Products Division
(renamed IBM Federal Systems in 1959) 
The AN/FSQ-7 Combat Direction Central, referred to as the Q7 for short, 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. The largest computer system ever built, each of the 24 installed machines:9 weighed 250 tons. The AN/FSQ-7 used a total of 60,000 vacuum tubes (49,000 in the computers):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.:179-181
The AN/FSQ-7 calculated one or more predicted interception points for assigning manned aircraft or CIM-10 Bomarc missiles to intercept an intruder using the Automatic Target and Battery Evaluation (ATABE) algorithm. Also used in the Nike AN/FSG-1 system, ATABE automated the Whiz Wheel (Felsenthal CPU-73 A/P Air Navigation Attack Computer) method used in manual command post operations.
The Q7 fire button launched the Bomarc, 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.:30-3 Later improvements allowed transmission of Q7 guidance to autopilots of manned fighters for vectoring to targets via the SAGE Ground to Air Data Link Subsystem (cf. bomber vectoring to a Bomb Release Point in 1965-1973 Vietnam via vacuum-tube analog computers.)
The first United States 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, Massachusetts 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) was based on the larger and faster Whirlwind II design, which was not completed and was too much for MIT's resources (MIT Lincoln Laboratory Division 6 still participated in AN/FSQ-7 development). Similar to the Q7, the smaller AN/FSQ-8 Combat Control Central was produced without an Automatic Initiation Area Discriminator and other equipment.:151
The experimental SAGE subsector, located in Lexington, Massachusetts, was completed in 1955, equipped with a prototype AN/FSQ-7 known as XD-1 in Building F. The third evaluation run with the XD-1 was in August and the prototype was complete in October 1955, except for displays. 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, Q7:57 1500 miles away. DC-1 at McGuire Air Force Base was the first operational site of the AN/FSQ-7:11:10 with consoles scheduled for delivery Aug-Oct 1956. Groundbreaking at McChord Air Force Base was in 1957 where the "electronic brain" began arriving in November 1958.
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 (cf. Operation Skyshield). The vacuum-tube SAGE network was completed (and obsolete) in 1963, and a system ergonomic test was performed 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.":9Back-Up Interceptor Control Systems (BUIC) were used to replace the AN/FSQ-7s::10 two remained at SAGE sites until 1983:9 including McChord AFB, and the Q7 at Luke AFB was demolished in February 1984.
The SABRE airline reservation system used AN/FSQ-7 technology. Q7 components were used as props in numerous films and television 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 and many others. The Computer History Museum displays several AN/FSQ-7 components.
MIT selected IBM as the prime contractor for equipment construction. 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. The Q7 had input/output devices such as:
Punched card data was transferred to and from the core memory as binary images. Only the rightmost 64 columns were transferred, with each row containing two 32-bit words. (The left columns could be punched using a special instruction.) Data were transferred to the line printer as a card image as well.:125
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 (Commonly referred to as Big Mem and little Mem). On the FSQ 7 memory 1 had 65,536 words and memory 2 had 4096 words. The FSQ-7 at Luke AFB each bank had 65,536 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.:27 Trigonometric sine and cosine functions used 1.4 degree precision (256 values) via look-up tables.:67
|"On Guard! The Story of SAGE"|
|AN/FSQ-7 used for Bomarc launch|
|"In Your Defense" (Col. John Morton, narrator)|
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
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 CommandNOTE: The film identifies "Direction Center" versus "Data Center".minute 5:15
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
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)
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 BitSavers.org)
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