IBM AN/FSQ-31 SAC Data Processing System

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The IBM AN/FSQ-31 SAC Data Processing System[3] (FSQ-31, Q-31, colloq.) was a USAF command, control, and coordination system for the Cold War Strategic Air Command (SAC). IBM's Federal Systems Division[3] was the prime contractor for the AN/FSQ-31s, which were part of the TBD 465L SAC Automated Command and Control System (SACCS),[4] a "Big L" system of systems (cf. 416L SAGE & 474L BMEWS([5] which had numerous sites throughout the Continental United States: "all SAC command posts and missile LCC's"[6] (e.g., The Notch), a communication network, etc.; and the several FSQ-31 sites including:

The FSQ-31 provided data to a site's Data Display Central[9] (DDC) "a wall display"[9] (e.g., Iconorama), and the FSQ-31 replaced the TBD at Offutt in 1960.[10] On February 20, 1987, "SAC declared initial operational capability for the SAC Digital Network [which] upgraded the SAC Automated Command and Control system "[7]


The FSQ-31 included:

  • Electronic Data Transmission Communications Central (EDTCC) at 4 "zone-of-interior headquarters bases" for EDT with "outlying" Remote Communications Centrals (e.g., routing "to RCC's, computer (DPC's), or the display devices.")[9]
  • Tape Controllers 1 and 2, connected to 16 IBM 729-V Tape Drives
  • Disk File Controller, which was a modified Tape Controller, connected to the
    • Bryant PH 2000 Disk File, which had 24 disks that were 39 inches in diameter, 125 read/write heads that were hydraulically actuated, and had a total capacity of 26 MB
  • IBM 1401, which controlled data transfers from unit-record equipment:
  • 2 IBM Selectric Typewriters, (I/O Typewriters) one of which was used for operational messages and the other for diagnostic messages and maintenance activities.
  • Advanced Display Console[10]
  • Drum Memory system with controller and two vertical drum memory devices. Each drum read and wrote 50 bits at a time in parallel so transferring data could be done quickly. The drums were organized as 17 fields with 8192 words per field for a total capacity of 139264 words. The motors that rotated the drums required 208 VAC at 45 Hz so a motor generator unit was required to change the frequency from 60 Hz. This added to the noise level in the computer room.
  • Rockwell-Collins modem[8]
  • Water chilling system for maintaining the liquid coolant temperature in the IBM 4020[3]

SACCS systems outside of the AN/FSQ-31 included the Subnet Communications Processor and the SACCS Software Test (SST) Facility at the Offutt command center (the backup SCP was at Barksdale AFB.)[12] SAC's QOR for the National Survivable Communications System (NSCS) was issued September 13, 1958;[13]:175 and in September 1960 the "installation of a SAC display warning system" included 3 consoles in the Offutt command center.[13]:218


The Q-31s were equipped with four 16 kiloword memory banks. The memory bank was oil and water cooled. Also considered as part of the memory subsystem in that they were addressed via fixed reserved memory addresses, were four 48 position switch banks, in which a short program could be inserted, and a plugboard, similar to the one used in IBM unit record equipment, that had the capacity of 32 words, so longer bootstrap or diagnostic programs could be installed in plug panels which could then be inserted into the receptacle and used. This served as a primitive ROM.

External images
terminal at Offutt command center
SACCS comm network


  1. ^
  2. ^ Wainstein, L. (June 1975). The Evolution of U.S. Strategic Command and Control and Warning: Part One (1945-1953) (Report). Institute for Defense Analyses. pp. 1–138. 
  3. ^ a b c Weik, Martin H. (March 1961). "Chapter II: Computing System Description". A Third Survey of Domestic Electronic Digital Computing Systems. Ballistic Research Laboratory. p. 0044 (start page). Report No. 1115. Retrieved 2014-04-01. 
  4. ^ Wohlman, John (1968). "An Aid to Command and Control". Computer-Generated Map Data. Air University Review. Retrieved June 20, 2006. 
  5. ^ title tbd. SAGE—Air Force project 416L—became the pattern for at least twenty-five other major military command-control systems… These were the so-called "Big L" systems [and] included 425L, the NORAD system; 438L, the Air Force Intelligence Data Handling System; and 474L, the Ballistic Missile Early Warning System (BMEWS). … Project 465L, the SAC Control System (SACCS) [with] over a million lines, reached four times the size of the SAGE code and consumed 1,400 man-years of programming; SDC invented a major computer language, JOVIAL, specifically for this project. … In 1962 the SACCS was expanded to become [WWMCCS] 
  6. ^ title tbd, SACCS - SAC Command and Control System. This is a Teletype system connecting all SAC command posts and missile LCC's. Its purposes are to communicate the status of SAC forces and transmit EAM's, also called 465L. 
  7. ^ a b SAC missile chronology
  8. ^ a b Coleman, DA. "[biographical anecdote]". Retrieved 2014-04-01. 
  9. ^ a b c Gorenstein, S. (March 15, 1963). A Simplified Queuing Model for the 465L System (Technical Memorandum) (Report). System Development Corporation. Retrieved 2014-04-02. All incoming messages to the EDTCC are automatically switched and routed to the designated locations. 
  10. ^ a b c "The IBM 4020 Military Computer" (PDF). IBM Federal Systems Division. 31 October 1959. Retrieved September 28, 2009. 
  11. ^ IBM 4020 documentation
  12. ^
  13. ^ a b Moriarty, J. K. (June 1975). The Evolution of U.S. Strategic Command and Control and Warning: Part Two (1954-1960) (Report). Institute for Defense Analyses. pp. 139–266.