Thanks to Tom Page for providing the images of this manual. In the manual, pages 2, 10, 38, 42, and 48 (rear cover) are blank. Please be aware that OCRing and manual checking are both error prone. This work is provided for your viewing pleasure by Ed Thelen. ;-)



1 January 1959 -
15 March 1965

This document contains information of a proprietary nature. Any use or reproduction of this document for other than government purposes is subject to the prior consent of International Business Machines Corporation.


Reproduction for non-military use of the information or illustrations contained in this publication is not permitted without specific approval of the issuing service (BuAer or USAF). The policy for use of classified publications is established for the Air Force in AFR 205-1 and for the Navy in Navy Regulations, Article 1509.

------- LIST OF REVISED PAGES --------

NOTE; The portion of the text affected by the current revision is indicated by a vertical rule in the left margin of a left-hand page and in the right margin of a right-hand page.


Heading Page
   1.1 Definition of AN/FSQ-7 and AN/FSQ-8 1
   1.2 Purpose of Manual 1
   1.3 Scope of Manual 1
    2.1 The Air Defense Problem 3
    2.2 Former System and Its Limitations 3
    2.3 Developing a New System 3
   2.3.1 1953 Cape Cod System 3
    2.3.2 1954 Cape Cod System 3
    2.3.3 Experimental SAGE Subsector 3
    2.3.4 Organizational Considerations 3
    2.4 Description of SAGE 4
    2.4.1 Combat Direction Center 4 Detection 4 Identification 5 Weapons Control 5
    2.4.2 Combat Control Center 7
    3.1 General Description 11
    3.1.1 Combat Direction Central 11
   3.1.2 Combat Control Central 11
    3.2 System Breakdown 11
   3.2.1 Input System 12 Gap-Filler Input Element 12 Long-Range Radar Input Element 14 Crosstell Element 14 Manual Data Input Element 14 Simplex Maintenance Console 14 Test Pattern Generator 14
    3.2.2 Drum System 14 Main Drums 16 Auxiliary Drums 17
   3.2.3 Central Computer System 17 Instruction Control Element 18 Selection Control Element 18 Program Control Element 19 Arithmetic Element 19 Internal Storage Devices 19 Input-Output Devices 19 Manual Controls and Computer Indicators 19
    3.2.4 Display System 20 Digital Displays 20 Situation Displays 20 Associated Equipment 22
    3.2.5 Output System 23 Output Messages 23 Output Control Element 24 Output Storage Element 25
    3.3 Physical Description 25
    3.3.1 Direction Center 25
    3.3.2 Control Center 25
    3.3.3 Combined Direction Center-Control Center 25
    4.1 Reliability Defined 35
   4.2 Maintenance Requirements 35
   4.3 Equipment Approach 35
    4.3.1 Duplexing 35
   4.3.2 Built-In Test Circuitry 36
    4.3.3 Special Test Equipment 36
   5.1 Philosophy of Organization 39
   5.2 Types of Manuals 39
    5.2.1 Theory Manuals 39 Introduction Manual 39 Theory of Programming Manual 39 Basic Circuits Manual 39 Special Circuits Manual 39 Logic Index Handbook 39
    5.2.2 Systems Manuals
    5.2.3 Maintenance Manuals 40
    5.2.4 Illustrated Parts Breakdown 40
   5.2.5 Schematics Books 40
   5.2.6 Special Test Equipment Manuals 40
   5.3 Organization of Manuals 40
   5.4 Other Reference Material 41
   5.4.1 Instruction Bulletins 41
   5.4.2 Program Library 41
   5.4.3 Military Reference Data Books 41 Electrical Standards 41 Mechanical Standards 41


Figure Title Page
2-1 Relationship of SAGE to the Air Defense System 5
2-2 Information Flow in the Sector 6
2-3 Information Flow in the Division 8
2-4 Major Means of Communication Between Operating Personnel and Automatic Equipment 9
3-1 Information Flow in the AN/FSQ-7 and AN/FSQ-8 12
3-2 Input System and Input Buffer Drum 13
3-3 Operational Block Diagram of Drum System 15
3-4 OD and CD Sides of Drum System 16
3-5 Computer and Auxiliary Devices 18
3-6 Display System and Display Drums 21
3-7 Facilities at a Typical Situation Display Console 22
3-8 Auxiliary Console 23
3-9 Output System, Block Diagram 24
3-10 SAGE System Direction Center Facility Requirements 26
3-11 Direction Center, Typical Floor Plans (4 Sheets) 27
3-12 Direction Center and Power Building 31
3-13 Control Center, Typical Floor Plans (3 Sheets) 31
3-14 Direction Center-Control Center and Power Building 33
3-15 Power Building for Combined Direction Center-Control Center 34
4-1 Typical Duplexing Arrangement 36
4-2 Outline of a Duplex Central 37

Chapter 1, Page 01




The AN/FSQ-7 Combat Direction Central and the AN/FSQ- 8 Combat Control Central are large-scale electronic digital computers manufactured for the United States Air Force by International Business Machines Corporation. These computers are assigned vital roles in defending continental United States against hostile attack from the air.


The purpose of this manual is to introduce the AN/FSQ-7 and AN/FSQ-8 data-processing systems by describing briefly what they are, what they do, and how they do it. Descriptions, whenever possible, are presented in general, non-technical terms so that persons with little or no technical background may attain a general, overall picture of the subject.

The final section of this manual introduces the related manuals that treat the specialized technical phases of the systems which comprise the AN/FSQ-7 Combat Direction Central and the AN/FSQ-8 Combat Control Central.


In introducing the AN/FSQ-7 and AN/FSQ-8, it is felt that a presentation of the events that brought above their establishment would enable the reader to gain broader appreciation of the overall situation. With the: in mind, therefore, the manual begins by defining the national air defense problem, and proceeds to describe the development of the Semi-Automatic Ground Environment (SAGE) air defense network, the AN/FSQ-7 Combat Direction Centrals and AN/FSQ-8 Combat Control Centrals that are the prime components of SAGE and the several major functional equipment systems that make up the centrals.

The final chapter lists and describes the various technical manuals in this series, and provides a brief description of several sources of supplementary reference material which will aid in further study of the AN/FSQ-7 and AN/FSQ-8.

Chapter 1, Page 02

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Chapter 2, Page 03




The problem of air defense is the protection of population, industrial areas, natural resources and retaliatory forces from hostile air attack. To accomplish this, it is necessary to determine what means are available or should be developed to provide maximum security under the greatest possible threat.


Formerly, the task of defending the United States against hostile air attack was performed by a manual ground environment system, and the functions of detection, evaluation, and interception were completely dependent on human operation. However, due to the increased speed capabilities of aircraft since World War II and the rapid progress in the field of missile development, the manual system of air defense was recognized as being completely inadequate to cope with such formidable means of attack. Recognizing the potentialities of these weapons during the early stages of their development, the authorities responsible for continental air defense saw the need for a rapid, accurate, automatic system of air defense.


The Air Force, in late 1950, enlisted the cooperation of various civilian organizations in its efforts to improve the capabilities of the United States air defense network. The overall program was known as the Continental Air Defense System (CADS) Project, under which civilian organizations helped to bring the national air defense system up to the best possible operating condition and made recommendations to ensure the system's continued effective operation. The air defense system was greatly improved by the CADS Project, but fell short of the Air Defense Command requirements for a vastly improved air defense system.

Simultaneously, studies were made on the combined use of digital computers and radar-data transmission equipment for application to air defense. The testing of a high-speed digital computer was recommended to the Air Force to provide information on the capabilities of such equipment to solve the ever-growing problem of air defense. The findings of this program led to many new concepts for solving the problem and resulted in the establishment of an experimental project which gave rise to the SAGE System. This project was developed is three major phases: the 1953 Cape Cod System, the 1954 Cape Cod System, and the experimental SAGE subsector.

2.3.1 1953 Cape Cod System

The 1953 Cape Cod System was composed of a computer known as Whirlwind I (WWI) and a Direction Center, along with associated radar equipment The purpose of this arrangement was to gather preliminary test data which would substantiate the concepts of the SAGE System then being planned. Emphasis was directed toward singling out obvious problem areas and attempting to correct whatever difficulties were encountered, rather than toward gathering complete statistical data on system operation. Consequently there was very little modification of equipment.

2.3.2 1954 Cape Cod System

The 1954 Cape Cod System was the same as the 1953 system except that radar network and mapping facilities were increased. Several minor improvement were incorporated in the operating positions within the direction Center. The primary objective was to supply statistical results on system capacity and accuracy.

2.3.3 Experimental SAGE Subsector

The experimental SAGE subsector, located in Lexington, Mass., was completed in 1955. It is equipped with a prototype AN/FSQ-7 Combat Direction Central: known as XD-1. A radar system provides a variety of inputs similar in number and type to those used in the SAGE System. An Air Force ground-to-air data link is connected to the output for experiments with data-link equipped aircraft.

The experimental SAGE Subsector provides experimental data on electronic reliability, computer pro grams, and operating procedures. It is organized to sup. port the regular functions of a Direction Center and is used to obtain operational approval and to determine required equipment modifications.

2.3.4 Organizational Considerations

To ensure adequate air defense for continental United States, air defense activities were established a various echelons of command and responsibility. The overall function was delegated by the joint Chiefs of

Chapter 2, Page 04

Staff to the Continental Air Defense Command (CONAD). The primary concern of CONAD is the protection of retaliatory forces, population, natural resources, and industrial potential during initial or sustained attacks by hostile forces. This defense must ensure successful counterattack by this country and must also ensure the eventual successful conclusion of hostilities.

To carry out its assigned tasks, CONAD delegated certain portions of the air defense mission to subordinate echelons. This delegation has geographical as well as operational applications.

The Continental Air Defense Command is presently organized into three Defense Forces, and this structure is reflected in the SAGE System. Each Air Defense Force is composed of a number of Air Defense Divisions. The Air Defense Division is relieved of direct supervision of groups and squadrons. However, its area of responsibility is large, making mandatory the minimizing of administrative and logistic responsibilities at this level. These responsibilities are delegated to the Air Defense Wing.

The area for which an Air Defense Division is responsible is normally composed of three or more sectors. The headquarters for the division is the Combat Control Center. The Air Defense Division exercises operational control of units designated for air defense operations within the division and is the level at which coordination with adjacent divisions is achieved.

The Air Defense Wing, with headquarters at the Combat Direction Center, has subordinate units that are primarily weapons and radars. The area of responsibility of the Air Defense Wing is called a sector. To perform the functions of air surveillance, identification, and weapons control, detailed information on all defense elements is continually maintained.


The SAGE System is the portion of the air defense system of continental United States that provides the means for semiautomatic processing of data and weapons control. The SAGE System (fig. 2-1) consists of the following:
  1. The facilities required to process and transmit air surveillance data from data-gathering sources to Combat Direction Centers.
  2. Combat Direction Centers, where air surveillance data is processed, evaluated, and developed into air situations at a sector level from which threat evaluation, weapons assignment, and appropriate weapons guidance orders are generated.
  3. The facilities required to transmit situation data from Combat Direction Centers to Combat Control Centers and other Combat Direction Centers.
  4. Combat Control Centers, where situation data from the Combat Direction Centers is processed, and from which the utilization of weapons resources can be monitored and directed.
  5. The facilities required to transmit instructions from Control Centers to Direction Centers and to forward divisional situation data to other Control Centers and higher echelons of command.

2.4.1 Combat Direction Center

The Combat Direction Center is an installation which contains all the equipment (including the AN/ FSQ-7) needed to execute the functions of air surveillance, identification, and weapons control. The function of the Direction Center is to receive, process, and develop air surveillance data at the sector level (fig. 2-2). On the basis of the sector air situation, the threat is evaluated, weapons are assigned, and orders are given. Information of importance to an adjacent Direction Center is communicated (crosstold) to that Direction Center automatically via ground-to-ground data links. A summary of the sector air situation is passed (forwardtold) from the Direction Center to the Control Center which has jurisdiction over its activities. Three specific operations are included in the overall function of the Direction Center in solving the air defense problem. These operations consist of detecting the approaching aircraft, identifying the aircraft, and exercising operational control of defense weapons. Detection

The detection of all aircraft approaching the United States is performed by a variety of units. Offshore units, such as AEW aircraft, picket ships, and Texas towers give early warning of approaching aircraft. Long-range radars and gap-filler radars spot and track all aircraft within or close to the United States. Reports of aircraft detected by the DEW lines in the northern parts of the continent are forwarded to the Combat Operations Center (COG) for dissemination to subordinate units of the SAGE System.

An important characteristic of the SAGE System is its flexibility to accept improvements in radar techniques and equipment as they evolve. The AN/FSQ-7 and the radar-data transmission equipments greatly reduce the time delays inherent in data processing and permit more effective use of data from many radars. Therefore, a large number of gap-filler radars can be used to provide an integrated, overall air picture.

Figure 2-1. Relationship of SAGE to the Air Defense System

Each Direction Center controls, and is connected with, all air defense radars that are geographically

Chapter 2, Page 05

located within the sector. These radars provide adequate radar coverage. The air situation picture for the entire United States, therefore, is continuously maintained by both a perimeter radar screen and a radar umbrella. Any aircraft entering or originating in the United States can be detected and tracked continuously. Identification

There are three main forms of aircraft identification: Mark X (IFF) signals, the Multiple Corridor Identification System (MCIS), and the flight plan (military or commercial).

Aircraft equipped with Mark X equipment identify themselves automatically and do not require further action for identification by components of the SAGE System.

The MCIS requires all aircraft entering the coastal areas of the United States to identify themselves by means of prearranged check words and check maneuvers, as well as to use only predesignated corridors in approaching the Air defense Identification Zone (ADIZ)

Flight plans are required of all military and commercial flights. These flight plans are inserted into the AN/FSQ-7 computers and are matched with radar returns, continuously and automatically, to aid in identifying the spotted aircraft. Computer programs record the number of times an aircraft deviates from its assigned course and notify appropriate personnel each time a deviation occurs. Weapons Control

The SAGE System is designed to utilize not only existing forms of weapons but also new and improved equipment as it becomes available. Interceptor, antiaircraft units, and guided missiles are presently the basic weapons used by the Direction Center in defense activities.

The air bases under the control of a Direction Center keep the center informed of their operational status, and computer programming indicates the number of weapons committed during any action. In this fashion, personnel at the center are kept up to date on the status of weapons available for assignment to targets.

Scrambled interceptors are given mid-course guidance by the computer and are aided in their return to base by computer-generated directions. Provisions are

Chapter 2, Page 06

Chapter 2, Page 07

made for both data links and voice channels to control interceptors.

Point-defense weapons form the system of weapons that supply concentrated fire-power to protect small areas containing important targets or large, industrial, and heavily populated areas. The present, basic point-defense weapons are antiaircraft units and Nike missiles. As other types of weapons become operationally available, they may be incorporated into the SAGE System with only minor changes required in the programming of the Direction Centers.

2.4.2 Combat Control Center

The tremendous weapons-control and data-processing capabilities of the AN/FSQ-7 Combat Direction Centrals in the SAGE Air Defense System clearly demonstrate the need for a semiautomatic means of monitoring and supervising the air situation at a level above that of the Direction Centers. To meet this need, each geographical division is provided with a Control Center.

The Control Center is equipped with an AN/FSQ-8 Combat Control Central. This equipment is basically the same as the AN/FSQ-7 Combat Direction Central, differing primarily to the extent that some of the input and output equipment is eliminated in the AN/FSQ-8, since it receives no raw radar data. Also, fewer display and drum facilities arc required at the Control Center. The function of the Control Center in solving the air defense problem is to combine, summarize, and display the air battle picture for the supervision of the several sectors within the division. (See fig. 2-3.) The major activities with which the Combat Control Center is concerned are:

  1. Evaluation of the nature, strength, and direction of the threat
  2. Supervision of the air battle
  3. Allocation of weapons to the sector, deployment of weapons, and use of augmentation forces
  4. Co-ordination with adjacent Control Centers
  5. Ordering conditions of alert for the division
  6. Ordering overall status for weapons in each sector
  7. Manual plotting of distant early-warning information
  8. Dissemination of defense warnings to civilian and military agencies
  9. Implementation of Security Control of Air Traffic (SCAT) and Control of Electromagnetic Radiations (CONELRAD) plans
  10. Forward air situation and status of the division to higher echelons of command

At the same time that each Direction Center in the division develops and displays its own picture of the air battle in its particular sector, the data is automatically forwarded to the Control Center. At the Control Center, the air situation for each sector is displayed both separately and cumulatively. In other words, the Control Center maintains displays of the air situation in each individual sector within the division and, at the same time, combines the several sector air situation pictures to present an overall picture for the entire division. Any change in the air situations of the sectors is reflected immediately on the displays devoted to the individual sectors. These changes also immediately alter the overall air situation picture for the entire division. Thus, personnel at the Control Center are provided with an up-to-the-minute picture of the air situation in the area for which they are responsible (fig. 2-4).

They are in the most advantageous position to observe developments, make decisions, and issue commands which will be most effective in neutralizing the threat. Should the air threat move into an adjacent area, the adjacent Control Center may be forewarned in time to meet the threat. In receiving the forewarning, the adjacent Control Center receives all pertinent data concerning the air situation with which it is apt to be faced. At the same time, this data is forwarded to the next higher echelon of command, which supervises the activities of the several divisions so that the air situation, on a regional level, may be summarized and kept up to date.

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Chapter 3, Page 11




The AN/FSQ-7 Combat Direction Central and the AN/FSQ-8 Combat Control Central are the basic building blocks of the SAGE System. It is around these equipments that all operations in the SAGE System revolve, just as it is around the SAGE System that the major air defense operations for continental United States revolve. To appreciate the critical positions of the AN/ FSQ-7 and AN/FSQ-8 in the air defense system, a more complete description of their operations must be made.

3.1.1 Combat Direction Central

The AN/FSQ-7 Combat Direction Central is the data- processing equipment installed in a Direction Center at the sector level of command, and may be called the first line of air defense in the continental United States.

The process of air defense may be broken down into a series of related functions such as detection, identification, tracking, weapons control, etc. To perform these functions efficiently, the AN/FSQ-7 Combat Direction Central is capable of assembling large quantities of diverse information from many sources. This information includes radar data, commercial and military aircraft flight plans, and weather data. The Viral f is also capable of processing data to identify and track all aircraft, friend or foe. The AN/FSQ-7 also directs antiaircraft batteries-,and all interceptors, manned or remote-controlled; to positions close enough to the target for the interceptor itself to complete the interception. In addition, the AN/FSQ-7 keeps all personnel fully informed about the air situation, alerts them to actions required, displays possible recourses for action, and continually computes and displays all subsequent changes to the original data.

3.1.2 Combat Control Central

The AN/FSQ-8 Combat Control Central is the data- processing equipment installed in a Control Center at the division level of command.

The functions of the Control Central are largely supervisory in nature. Personnel at this echelon of command are responsible (1) for monitoring the action in each of the sectors comprising the division and (2) for making decisions relating to the allocation of weapons. In addition, personnel at the Control Central are responsible for co-ordination with other Control Centrals and for presenting the divisional air situation to higher echelons of command.


The huge data-processing computers that make up the principal equipments (see fig. 3-1) of the ANA FSQ-7 Combat Direction Central and the AN/FSQ-8 Combat Control Central are broken down into sever major systems through which all data is processed. They are:
a. Input System
b. Drum System
c. Central Computer System
d. Display System
e. Output System
f. Power Supply and Marginal Checking System
g. Warning Light System

The first five systems listed above are integral part: of the data-processing operations of the AN/FSQ-7 and the AN/FSQ-8 and execute functions within themselves which contribute to the overall operational solution of the air defense problem. The two latter systems listed above are not directly concerned with the defense functions of either Central.

For purposes of uniformity in design, production and maintenance, the AN/FSQ-8 equipment installed at the Control Center is almost identical to its counterpart the AN/FSQ-7 at the Direction Center. However, because of functional differences, certain portions of the equipment at the Control Center are either made inoperative or entirely omitted.

The Combat Control Central requires fewer operating personnel and has fewer display consoles than the Combat Direction Central. The Combat Control Central does not process raw radar data; therefore, the equipment required for receiving and processing radar data is unnecessary at these installations. Likewise, the amount of manual data input equipment is reduced. It follows logically that the computing capacity of the AN/FSQ-8 will not be as heavily committed as that of the AN/FSQ-7. Therefore, the Combat Control Central is able to assume additional activities in the future as the needs arise.

Chapter 3, Page 12

The discussion of the various systems in this manual is brief, general, and designed merely to acquaint the reader with the overall functions of the systems. For a complete detailed discussion of the various systems, the reader is directed to the related manuals devoted specifically to the various systems. These manuals are identified in Chapter 5.

3.2.1 Input System

The Input System of the AN/FSQ-7 Combat Direction Central receives automatic and manual input data from various sources, processes and assembles the data into a form compatible with computer requirements, and places the information on the input drum. Here, the data is temporarily stored until the computer program calls for it.

The Input System comprises four elements (fig. 3.2), which are named for the types of input data they process:

- long-range radar input (LRI),
- gap-filler radar input (GFI),
- crosstell (XTL) input,
- and manual data input (MDI).

Input data to the AN/FSQ-7 is transmitted automatically, from radar equipment. XTL information from other Centers is also sent automatically. Certain air surveillance, status, and other data received sporadically or at an extremely slow rate can be inserted manually into the machine. This slow-changing data is received at the Direction Center by voice telephone or by manually operated teletype equipment, processed by MDI operators, and inserted into the AN/FSQ-7 through card machines.

The XTL element automatically receives and processes digital data from the AN/FSQ-7 Combat Direction Centrals that are within the jurisdiction of the Combat Control Central and, also, from other Combat Control Centrals. The MDI element processes relatively slowspeed, low-priority input data from within the Central and is the means by which human commands and decisions are introduced into the computer.

In addition to the four input elements, the Input System is also equipped with a test pattern generator (TPG), used for input channel testing, and the simplex maintenance console in which the control panels for the channels of the input elements and the TPG are mounted.

The Input System at an AN/FSQ-8 Combat Control Central is composed of only two major elements, the XTL element and the MDI element. The TPG and the simplex maintenance console are employed in the AN/ FSQ-8 in exactly the same manner as in the AN/FSQ-7. Gap-Filler Input Element

Slowed-down video equipment transmits range and azimuth data over data circuits to the AN/FSQ-7. A digital-data receiver demodulates the telephone line signal and separates pulses representing azimuth, range, and target. Separate magnetic-core counters count the azimuth and range pulses. The azimuth and range count in these counters at the time of a target pulse specifies the polar co-ordinates of a target with respect to the radar location.

A radar-mapping technique employing a plan position indicator (PPI), a mask, and a photocell removes areas of unwanted data, such as ground clutter, from the system. A mapper console displays all radar returns on a PPI presentation, allowing an operator to evaluate the target indications and to eliminate those that are undesirable.

Chapter 3, Page 13

Each target appears on the mapper console cathode-ray tube screen as a blue flash followed by a long persistent yellow glow. A photomultiplier tube with a filter, mounted above the screen, generates mapped target pulses from the blue flashes only. The operator, by painting a liquid which is opaque to blue light over unwanted targets, prevents their presentation to the computer. The operator can see the yellow glow, but the photomultiplier tube cannot detect the blue flash through the filter and the mapping liquid. The GFI drum acts as a reservoir for gap-filler radar data. This data is stored in the drum until requested by the computer.

Chapter 3, Page 14 Long-Range Radar Input Element

Fine grain data (FGD), Mark X, and height-finder messages are sent to the LRI element of the AN/FSQ-7 over telephone data circuits. The data-circuit messages are received at the Center by digital-data receivers and are placed in core-shift registers which assemble the messages. At the instant the drum is ready to accept a message, a drum-demand pulse is sent out to sense the status of the registers. When the presence of a complete message is sensed, the words in the registers are prepared for transfer to the drum. The first half-message is read to the drum and is immediately followed by the second half-message.

The LRI drum stores FGD, Mark X, and heightfinder messages until the computer is ready to use them. Crosstell Element

The XTL element of the Input System receives information in the form of binary coded messages over telephone circuits. The messages are transmitted from their source at a high, signal repetition rate on a partyline arrangement and, therefore, include a specific address code directing the message to a particular site or sites, as the case may be, or an all-parties address which directs the message to all Centrals on the line. The XTL input element automatically checks the address, accepting only those messages that are addressed to its Central or to all Centrals.

In the strict sense of the word, the term crosstell refers only to the exchange of information between Centrals of equal command; i.e., between AN/FSQ-7 Combat Direction Centrals or between AN/FSQ-8 Combat Control Centrals. The XTL element of the Input System in the Combat Control Central, however, also receives information from the subordinate Combat Direction Centrals. This operation (from Direction Central to Control Central) is called forwardtelling and is distinguished from crosstelling. However, since both crosstold messages from other Control Centrals and forwardtold messages from Direction Centrals are accepted by the XTL element of the Control Central, both are considered to be the same for purposes of discussion in this chapter. Manual Data Input Element

The fourth major element of the Input System is the MDI element. The following discussion describes in general terms the functions and components of the MDI element and its relationship to the Central Computer System and other sources of data utilized at the Central. Because of this relationship to other sources of data, a brief discussion of the part each data source plays in the process of transferring data within the Central is also presented here.

The overall function of the MDI element is to process input data which is manually introduced into the machine. This data includes four general categories of information:

  • information entered on IBM punched cards and read into the MDI element by means of computer entry punches;
  • track data appearing on display scopes, picked up by a manually operated light gun, and fed back into the MDI element;
  • messages initiated by operation of intervention switches;
  • and status signals to the Central Computer, indicating the active or standby status of certain elements and channels.

To process these various inputs, the MDI element is divided into two sections, each with its own particular functions. These two sections are the drum entry section and the direct entry section. Due to the disparity in the speeds of assembling messages, each of the two sections processes data originating from different sources. Simplex Maintenance Console

The simplex maintenance console provides centralized facilities for controlling the operation of other simplex equipment in the Input System (see Ch 4, 4.3.1). This control function is centered in the ability of the console to control the power flowing to those equipments. Specifically, it controls power distribution td units receiving power from the circuit breaker unit, the data inputs and the data outputs of the input channel units, and the marginal checking operations in the simplex units. Test Pattern Generator

The test pattern generator (TPG) performs the function of checking the input elements of the Input. System for possible malfunctions. To accomplish this the TPG causes test signals resembling telephone line messages to be generated into the input elements. Channel control panels on the simplex maintenance console control this channel equipment. Test signals from the TPG may be substituted for actual telephone line data by means of switches located on each control panel of the simplex maintenance console.

The test pattern generator is capable of being operated either by manual control alone or by both manual control and computer control together. Messages can be initiated, terminated, or continuously repeated under either manual or manual-computer control. During certain operations, the TPG is under complete manual control, the messages being composed, initiated, and terminated by manually set switches. During certain other operations, the messages are composed manually but are initiated by instructional pulses sent out by the Central Computer.

3.2.2 Drum System

The Drum System (fig. 3-3), composed of group of magnetic storage drums and associated control

********* pages 15 and 16 were recovered from microfilm, and a bit noisey ********

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Main Drums 311-31Z I 3-12-11 CH 3 and transfer circuitry. performs two important functions. It acts as a time buffer storage system between the Central Computer System and the Input. Output, and Display Systems. and it am as an auxiliary memory for the computer. During normal operation of the Central, the Drum System handles most of the information being passed between the other systems but in no way alters this information. (As a storage device, it performs no computations.)

> The Drum System is composed of six main drums and six auxiliary drums. All drums are identified by names based on their functions in relation to other systems. The six main drums are designated as follows: the LOG drum, the MIXD drum, the RD drum, the TD drum, the AM-A drum, and the AM-B drum. The letters used in the designations are the initial letters of the equipments which they serve. For example, the LOG drum handles the transfer of data to and from the LRI (long-range radar input), OB (output buffer), and GFI (gap-filler radar input) elements of the Central. Likewise the MIXD drum is concerned with the MDI (manual data inputs), IC (intercommunication), XTL (crosstell), and DD (digital display) elements. The RD transfers radar data, while the TD drum accommodates track displays. The AM-A and AM-B drums are auxiliary memory (AM) drums A and B.


The data accommodated by each drum is assigned to logical drum divisions known as fields. The main drums have a total of 39 fields, 9 fields on the RD drum and 6 fields on each of the other drums. Of these fields, three (LRI. GFI, and RD) are not utilized in the functional operations of the AN/FSQ-8 Combat Control Central, because the Control Central is not involved in processing the raw radar data to which these fields are devoted in the Direction Central. Consequently, these drum fields are available for use as auxiliary storage devices at the Control Central. Main Drums
The operations of the main drums may be separated into two major categories: the operations involved in the exchange of information with the Central Computer System and the operations involved in the exchange of information with the other systems. Information transfers between the main drums and the Central Computer System are known as CD (computer-to-drum) operations. Information exchanges with other systems are known as OD (other-than-computer-to-drum) operations (fig. 3-4).

The primary functions of the main drums are to serve as temporary storage devices for the transfer of information to and from the Central Computer and to discharge this information at speeds compatible with the surrounding systems. The drums are capable of storing information as long as necessary. Information is written into and read out of the drums without alteration. Tactical data introduced into the Drum System from the Input System for transfer to the Central Computer System arrives at random intervals in large quantities. The drums store this data until it is requested by the Central Computer System Tactical information that has been processed by the Central Computer System is written onto the drums at a high rate of speed, stored temporarily, and then read off to other systems at speeds compatible with their operations.

Since the access time to data stored on drums is longer than that of data stored in computer memory, the computer transfers large blocks of information from drums to core memory before they will be needed. Thus, the high speed of computer arithmetic operations is not retarded. Besides functioning as storage devices, the main drums generate timing pulses for use by the Input, Output, and Display Systems. These timing pulses synchronize the joint operations of the drums with the systems named above during the transfer of data. When data transfers are not in process, these same systems utilize drum timing pulses to control their own internal operations.

In addition, the Drum System stores intercommunication data for transfer to the standby Drum System and standby Central Computer System (4.3.1). When

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maintenance operations are to be performed on the active Drum and Central Computer Systems, the operations of the active systems are switched to the systems that have been in a standby status. To shorten the time consumed in the transfer of data, intercommunication between the active and standby systems is maintained constantly. As a result, the standby equipment is kept as up to date as possible with the operations of the active equipment. Another use for the intercommunication function is that it enables the standby computer to check the operations of the active computer while they are being performed. Auxiliary Drums

The six auxiliary drums are located in the auxiliary drum housing and control unit. They exchange information exclusively with the Central Computer System. This exchange is effected via the CD circuits of the auxiliary drums. It is mandatory that the Central Computer System be able to select rapidly any data it desires from the auxiliary drums. To accomplish this, an address- controlled method of reading out of and, writing onto the auxiliary drums is employed. This method permits the Central Computer System rapid access to a specific register.

As an auxiliary memory, the Drum System can store information indefinitely. The drums performing this function are accessible only to the Central Computer System, since the other systems have no need of auxiliary storage facilities. Computer programs, subprograms, tables of reference data, etc., are the types of data most generally stored on the auxiliary drums.

Central Computer System programs and subprograms, for the most part, are too extensive to be stored entirely in the memory of the Central Computer System; therefore, additional storage space is provided in the Drum System. The access time of data stored on drums, while slower than the access time of data stored in computer memory, is appreciably faster than the access time of data stored on card and tape machines. The drums, therefore, fulfill the requirements of storage capacity at a medium access time.

3.2.3 Central Computer System

The Central Computer System (fig. 3-5) is made up primarily of a general-purpose, high-speed, singleaddress, binary digital, stored-program computer with associated input-output (IO) devices. The Central Computer is designed to accept large amounts of military tactical data and to process the data quickly. Generally speaking, the purpose of the Central Computer is to correlate and process data and to transfer the results to other systems of the Central.

The Central Computer is capable of adding, subtracting, multiplying, and dividing. More complicated operations such as extracting square roots and evaluating complex variables can be performed by combining the basic arithmetic operations. The computer is designed to respond to simple stereotype instructions, each of which causes the computer to perform a single arithmetic operation. An extended sequence of such instructions, resulting in the solution to a problem, is called a program.

When solving any given problem, the Central Computer actually uses only the addition process, reducing all other processes to types of addition. This is more easily accomplished in a computer by utilizing the binary rather than the decimal number system. The binary system is based on a 1 or 0 (yes or no) principle and, consequently, requires circuits with two stable conditions to indicate a 1 or a 0. The decimal system, involving 10 digits (0 to 9) would require circuits with 10 stable conditions.

The function of the Central Computer System is to process algebraically and logically the military tactical data supplied to it by the Input System via the Drum System, transferring the results back to the Drum System for subsequent distribution to the Display and Output Systems.

In addition to processing data, the Central Computer System operates as the main control for the Central. As data is being processed, the Central Computer generates signals, as instructed, and sends them to the Drum System for utilization by the Input, Display, and Output Systems. These signals control the flow of data between systems, initiate operational cycles, set up control circuits for the coming operations and, in general. synchronize the actions of each system with those of the Central Computer System.

Functionally, the Central Computer System is divided into seven groups:
a. Instruction control element
b. Selection control element
c. Program control element
d. Arithmetic element
e. Internal storage devices
f. Associated IO units
g. Manual controls and computer indicators

The instruction, selection, and program control elements sequence, co-ordinate, and control all processes in or allied with the operation of the computer. The entire instruction control element and a part of the program control element govern internal computer operations, while the selection control element and the remaining part of the program control element govern external computer operations primarily connected with 10 devices.

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The arithmetic element performs arithmetic processes using numerical data as instructed by the program. The associated 10 units are commercial IBM machines modified for use with the computer and are not to be confused with the Input and Output Systems of the Central. The manual control facilities enable personnel to start, operate, shut down, and service the computer. Instruction Control Element

The instruction control element furnishes command pulses to the computer in correct sequence, enabling the computer to carry out the programmed instructions stored in the computer memory element. Functionally, the instruction control element decodes each instruction and generates the commands needed to carry out the processes indicated by the instruction. Physically, the instruction control element is divided into three sections: the instruction decoder, the pulse generator and control, and the command generators. Selection Control Element

The selection control element is divided into four sections: the index interval register, the Operate-Select Sense (PERSELBSN) matrix, the break command generators, and the control circuits.

The selection control element synchronizes, controls, and directs data being transferred between the computer memory element and the several IO units including the Drum System. Prepared instructions, set ting up control circuits in the selection control element must be performed in advance of the actual transfer of information. This enables the information transfer t< be properly initiated and processed.

The selection control element also incorporate: circuits which permit the Central Computer, directed by a specific program, to perform certain operations affecting the electromechanical units allied with the 10 units and the several other electromechanical units in the system. In addition, the selection control element determines existing conditions in the Central and directs the operations of the computer accordingly.

Chapter 3, Page 19 Program Control Element

The program control element, in order to procure specific instructions, controls the selection of internal storage devices and such information as may be required by an instruction. In addition, the program element sequences the transfer of each instruction stepped out of the internal storage devices at the proper moment.

In guiding the processing of information, the program element co-operates with other elements of the computer. The instruction control and program elements together sequence and control the internal information-processing operations. The program and selection control elements together co-ordinate and effect the external transfer of information between the computer and other systems of the Central. The program element, therefore, contains circuits associated both with the internal control operations of the instruction control element and with the external control operations of the selection control element. Arithmetic Element

The arithmetic element contains circuits and registers which perform mathematical computations on numerical data. The element is divided into two separate portions which are composed of identical groups of circuits and registers and are known as the left arithmetic unit and the right arithmetic unit.

Primarily, the arithmetic element employs the four basic arithmetic operations (addition, subtraction, multiplication, division) in the performance of its functions. Operands for the calculating processes are obtained from the computer memory element. The setting up of arithmetic operations is governed by add-class and multiply-class instructions which provide command pulses from the instruction control element. The result of the calculations is either retained in the arithmetic element for further processing or transferred to the memory element for storage until required by a subsequent program. Internal Storage Devices

Three separate storage devices are contained within the computer: the core memory, the test memory, and the real-time clock. The core memory and the test memory furnish storage space for and permit quick access to instruction and information words. The real-time clock generates real-time information in the form of pulses.

There are two core memory elements contained in the computer. These elements are high-speed storage devices that are able to store and facilitate rapid access to thousands of binary words. Each of the core memory elements is divided into three units: a left memory unit. a core memory array unit, and a right memory unit. Both memory units are composed of equipment associated with the transfer of information between the core memory elements and other systems as well as the computer itself. The core memory units are composed of actual arrays of ferrite cores in which information is stored.

The test memory is composed of 19 registers and other equipment associated with the transfer of information between the test memory and the computer Physically, certain portions of the test memory are located in two separate units. The plugboard control panel and the control switches are located on the duplex maintenance console, and the addressing and readout control circuits are located in the left arithmetic unit. Input-Output Devices

The IO devices of the Central Computer System are composed of card machines, magnetic tape units, and the IO register. In order to eliminate confusion brought about by similarity in terminology, a distinction between the Input and Output Systems and IC devices should be made.

An input device associated with the computer may be defined as a unit which transmits data directly into the computer. An output device is a unit which receive data directly from the computer. Certain units, because of the nature of their functions, may be considered a; being both input and output devices. The Input System and the Output System do not deal directly with the computer, as the data for these Systems must first pass through the Drum System. Manual Controls and Computer Indicators

The manual controls and indicators of the computer are situated on the duplex maintenance console and on the duplex switching console, as are the controls and indicators for the other systems of the Central These controls and indicators supply maintenance personnel at the Center with a means of manual control for loading initial operating programs, loading certain reliability and diagnostic test programs, and monitoring the operations of the major registers and circuit in the associated equipment.

The duplex maintenance console contains the majority of the controls and indicators for the manual operation of the Central Computer System. The alarm and neon indicators on the console show the status of the computer, and virtually all manual program and checking operations are affected by means of the con sole controls.

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The duplex switching console is used by maintenance personnel to establish the status, active or standby, of the separate sets of duplex equipment. Each computer transfers status data to the duplex switching console. This data activates indicators and alarms, permitting maintenance personnel to determine the operating condition of each computer and to make quick decisions pertaining to duplex switching operations.

3.2.4 Display System

The Display Systems of the AN/FSQ-8 Combat Control Central and the AN/FSQ-7 Combat Direction Central are similar in both physical and functional aspects. The chief physical difference is that the Control Central utilizes fewer display consoles. Since no raw radar data is processed by the AN/FSQ-8, the necessity of employing consoles for the presentation of a great many individual tracks and. raids as they are received from radar installations is eliminated.

Information processed by the computer is sent via the display drum fields to the Display System, where it is converted as required and presented on cathode-ray tube (CRT) displays to the operators of the. Figure 3-6 shows the Display System, the associated drums, and the tie-ins to the MDI element.

The equipment contained in the Display System, for purposes of this discussion, is divided into the following major groups: the digital displays, the situation displays, and associated equipment. The digital and situation displays are made up of consoles housing CRT's which present a picture of the air situation to an observer. The associated equipment is made up primarily of various components connected with the operational functions of the displays.

The Display System provides the means by which the air situation of the area supervised by the Center is visually presented to human observers. This is accomplished by means of special CRT's mounted in specially constructed and equipped consoles.

Data is first accepted by the Input System and is subsequently transferred to the Display System via the Drum and Central Computer Systems. The tracks and raids representing the air situation are consolidated and converted into larger common co- ordinates for display at the consoles. Since all such data is received from the computer in binary form, the Display System converts the data from the binary form to a system of letters, numerals, vectors, and symbols. This conversion permits the presentation of a display which is more readily viewed and interpreted by the observer.

The console operator observing the air situation messages presented on the CRT may act on the information in several ways. The operator may communicate with the computer by requesting information from the computer, or by feeding back information in answer to a request from the computer. He may instruct the equipment to transfer a message to the console of another operator. These operations are possible through the use of manual-intervention switches and light guns located on the consoles. Telephone facilities located at the console are also available to the operator for communication with other personnel within the Center He may also communicate beyond the area of the Center by wire and radio telephone circuits.

The Display System employs two basic types of CRT displays for presenting the visualized air situation to the human observer. They are the digital displays and the situation displays. The CRT's for these displays are mounted in various types of display consoles located at selected operating positions in the Center. Typical consoles are equipped with a situation display (SD) scope, a digital display (DD) scope, and various manual- intervention (MI) switches, alarms, and warning lights. Many consoles are also equipped with a light gun and telephone facilities (fig. 3-7).

In addition to the display consoles, the equipment of the Display System encompasses various types of associated equipment, including auxiliary consoles (fig. 3-8), which aid the Display System in the performance of its functions. Digital Displays

The DD scope is a 5-inch CRT mounted in the upper right portion of the display console (see fig. 3-7). Supplementary data that is either too voluminous or too slow-changing to warrant its presentation on the larger pictorial SD screen is presented on the DD screen. The information appears as a tabular array of characters and symbols and, unlike the situation display, changes only when the computer orders a change due to, for example, the presentation of new information. Barring receipt of instructions from the computer to the contrary, the digital display remains indefinitely.

Digital display data is processed by the computer and transferred in binary form via the Drum System to the Display System. Since data in binary form is difficult for an observer to interpret, the binary information is converted to analog voltages which, in turn, are converted to the visual display presented on the face of the DD CRT. Situation Displays

The situation display scope is a 19-inch CRT mounted in the center portion of the display console. A current plan- position map of the rapidly changing air situation which shows correct geographical relation, between fixed points and moving targets is presented on this scope. Supplementary descriptive data in the form of vectors and special symbols is positioned next to specific points and targets for identification purposes

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Figure 3-6. Display System and Display Drums

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The 19-inch CRT used for the situation display is not a conventional-type tube. It is a large, special-purpose tube which is capable of generating complete individual characters, drawing vectors, assembling the characters and vectors into message patterns, and positioning the entire message pattern in the proper place on the screen of the tube. The result viewed by the observer is an orderly arrangement of message patterns, each message consisting either of a single character m4 a group of characters.

All SD messages are rewritten on the face of the CRT at short, regular intervals. If the basic data has not changed or been superseded, the display is continually repeated in the same position. If, on the other hand. the information has changed, the display is corrected. It this way, the console operator is presented with air situation changes within an extremely short time after they occur. Associated Equipment

The associated equipment utilized by the Display System is made up of various components, each with it own special functions. Because detailed explanations o this equipment are n, be found in the Display System theory manual, all that need appear here is the following list of the equipment:
a. Command Post console
b. Auxiliary consoles
c. Signal data patching panels
d. Photographic recorder-reproducer
e. Situation display camera
f. Display tester
g. Situation display consoles

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The associated equipment is connected with the situation displays and the digital displays either physically, optically, or by signal flow. The situation display consoles, for example, provide the housing for the tubes and the devices needed to control their operations. Certain displays are equipped with either an SD camera element or with a photographic recorder-reproducer (PRR) element (optical connection). Since it sends signals to the Display System, the display tester element (DTE) a connected to the displays by signal flow.

3.2.5 Output System

The Output System (fig. 3-9) is made up primarily of two main elements:
- the output control element
- and the output storage element.
These two elements perform all functions of the Output System. In performing these functions, the Output System relies to a great degree, as do the other systems of the Central, on certain facilities of the Drum System.

The Output System transfers tactical information from the Center to other air defense installations. Having formulated an output message, the Central Computer System transfers the message to the output buffer (OB) fields of the LOG drum in the Drum System. The Output System then accepts the message from the OB fields and transfers it to the appropriate telephone terminal equipment for transmission to its destination. Output Messages

An output message is a communication transmitted from the Center to other vital installations Concerned with the air defense problem. Three basic types of messages are processed by the AN/FSQ-7 System and are stored in separate output storage sections before transmission:
  • Ground-to-air (G/A) messages, which are sent to manned interceptors and guided missiles (the AN/ FSQ-8. however, does not transmit G/A messages);
  • ground-to-ground (G/G) messages, which are intended for crosstelling to adjacent centers, higher echelons, and remote radar sites;
  • and teletype (TTY) messages, which arc used for communication to higher echelons and antiaircraft batteries.
The messages may be grouped into one of three categories, depending on the intended destination of the message; that is, into crosstell, back tell, and forwardtell messages.

Output messages transmitted from one Center to other centers at the same echelon of command are known as crosstell messages. Thus, messages from one AN/FSQ-7 to other AN/FSQ-7's, and from one AN/ FSQ-8 to other AN/FSQ-8's, fall into this category. The

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messages are composed by the computer and sent via the Drum System to the Output System for automatic transmission to adjacent Centers over automatic (G/G) party-line telephone lines.

Backtell messages are those communications that are transmitted to facilities at subordinate echelons of command. Thus, a message from an AN/FSQ-7 to a radar site, for example, would be a backtell message. In the same sense, a message from an AN/FSQ-8 to an AN/FSQ-7 would also be a backtell message. At the AN/FSQ-8, however, backtell messages are presently carried over voice telephone lines only and therefore are not a function of the Output System.

Output messages which relay tactical information to higher echelons of command are known as forwardtell messages. Teletype equipment is one means of communicating with higher echelons not equipped with AN/FSQ-7 Combat Direction Centrals or AN/FSQ-8 Combat Control Centrals. Output Control Element

The output control element is concerned with the flow of output message words transferred to the output storage element from the OB fields of the LOG drum in the Drum System. The output control element also provides the Central Computer System with specific information utilized in the air defense program as an aid in regulating the timing of output messages. In addition, the output control element provides visual indications of possible alarm conditions in the Output System as a whole. Finally, the output control element controls the test equipment used in the Output System This equipment assists in locating malfunctions within the Output System and also aids in checking certain elements of the Input System.

Chapter 3, Page 25 Output Storage Element

The output storage element is composed of six distinct sections for the temporary storage of output message words: ground-to-air frequency division (G/A-FD), BOMARC 1, BOMARC 2, ground-to-ground (G/G), ground-to-air time division (G/A-TD), and teletype (TTY). Each section, generally speaking, accommodates a different type of output message and is named accordingly.

The G/A-FD and G/A-TD storage sections receive and temporarily store output messages that are to be sent from the Center to manned interceptors. This storage section transfers such messages to the telephone terminal equipment utilized in relaying messages to automatic, radio, data-link transmitters and thence to the interceptors.

The BOMARC 1 and BOMARC 2 storage sections receive and temporarily store output messages intended for guided missiles. The transfer of such data to its final destination takes place in the same manner as for G/A messages.

The G/G storage section receives and temporarily stores output messages that will be sent to other Centers. It transfers these messages to the telephone terminal equipment utilized in transmitting information to sites that have automatic input equipment.

The TTY storage section receives and stores output messages that will be transmitted to higher echelons or to remote nonautomatic sites. It transfers these messages to telegraph terminal equipment used to send output data to installations equipped with teletype receivers.


Combat Direction Centers and Combat Control Centers in the SAGE System are generally located on established military installations maintained by the Air Force, and are logistically supported by the bases upon which they are tenants. Figure 3-10 indicates the facility requirements necessary for the operation of typical Direction Centers and Control Centers.

3.3.1 Direction Center

A typical Direction Center (DC) building is four stories high, 150 feet square, shock-resistant, and contamination proof. There is no standard building type, because of differences in equipment, design, etc. This condition is brought about by the fact that, as the centers are constructed and equipped, each succeeding site receives improved, modified equipment. Moreover, these improvements, plus new concepts of efficiency and ease of operation, have necessitated a complete redesign of the basic building, and new DC buildings will be three stories high and measure 270 feet by 150 feet.

A typical floor plan of the original Direction Center is shown in figure 3-12. The associated power and air-conditioning equipment building (fig. 3-12) is a 1-story structure, 110 feet square, and approximately 21 feet high. It is connected to the Direction Center by a 22-by-100-foot bay that provides for storage and maintenance space, including a throughway for steam, water, and power lines. Adequate fuel storage is provided for the operation of the power plant.

Typical support facility requirements for a Direction Center are:

  1. Administrative facilities
  2. Officer quarters
  3. Airman quarters -
  4. Officer mess and club facilities
  5. Airman mess and club facilities
  6. Post exchange
  7. Recreational facilities
  8. Motor maintenance facilities
  9. Installation administration and shops
  10. Supply warehouses
  11. Utilities and heating facilities
  12. Security facilities
  13. Officer and Airman family housing

3.3.2 Control Center

The typical Control Center (CC) building housing the AN/FSQ-8 Combat Control Central is a 3-story structure of the same type construction as the DC building. As is the case with DC buildings, the CC building has been redesigned, making it a 2- story building. The power and air-conditioning equipment plant and the fuel storage system are essentially the same as for the Direction Center. The support facilities necessary for a Control Center are the same as those for the Direction Center. For a typical floor plan of the original Control Center, see figure 3-13.

3.3.3 Combined Direction Center-Control Center

In certain instances, it has been found feasible to establish a Direction Center and a Control Center at the same location. The combined DC-CC building. shown in figure 3-14, consists of the two buildings described above, connected by a 1-story building 150 feet by 30 feet and framed to provide for possible expansion by the addition of one or two more levels

The power and air-conditioning plant is a stepped. 1-story building 220 feet by 150 feet, half of which is approximately 25 feet high, and the other half of which is approximately 15 feet high. It is located near the Operations Building. A covered passage for cables and piping connects the two buildings (fig. 3-15).

Fuel storage and support facilities for the DC-CC site are the same as those described for the DC and CC sites.

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One of the main requirements of the SAGE System is that its components be reliable 24 hours per day. This reliability is achieved through several concepts, the most basic of which is duplexing critical equipment.

Both the AN/FSQ-7 Combat Direction Central and the AN/FSQ-8 Combat Control Central utilize tens of thousands of electron tubes and associated circuitry. Of these, more than half are processing air defense data at any given time. To assure continuous functioning of both Direction Central and Control Central, the following precautions are incorporated into each as basic features:

a. Duplex installation of critical equipment
b. Marginal checking of component deterioration
c. Rigid control of component operating temperatures
d. Circuit designs that permit large component value changes before failure
e. Reliable components

Because of the physical nature of the equipment and the importance of its function, the requirements for optimum reliability cannot be over-emphasized. It is one thing to develop equipment designed to solve the problems of air defense. It is something else again to be able to rely on that equipment for continuous operation with accurate results. The security of the nation demands that the SAGE System, in all its aspects, be unerringly reliable.


The AN/FSQ-7 and AN/FSQ-8 are high-speed, electronic, digital computers of extreme complexity. Consequently, normal maintenance procedures are inadequate for preventing computer failures. If an error occurs while the computer is performing some intricate computation, a more systemic approach to maintenance is required. This approach is realized by the utilization of maintenance programs. A maintenance program is capable of checking out computer system circuits and components very rapidly, and provides audible and visual indications that enable maintenance personnel to pinpoint failure locations.

Error detection by the use of programs has distinct advantages. A program can be changed easily when the computer or any auxiliary components are changed. A program can be constantly improved. No extra equipment is required since the program uses the facilities that are already available. A program uses the machine in a more normal manner than does test equipment. A program that has been checked and accepted as a good maintenance tool is not subject to deterioration. B3 contrast, standard test equipment may be checked and accepted only to become unreliable shortly after being placed in actual use.

Maintenance programs are divided into two main classes, reliability programs and diagnostic programs. Maintenance programs used to detect the existence of errors are called reliability programs. A reliability program checks all or part of the computer for correct operation. Maintenance programs used to isolate machine failures known to exist are called diagnostic pro grams. A diagnostic program locates the machine fault as closely as possible.


To assure the greatest possible degree of reliable continuous performance by the computers, certain special approaches were developed in relation to the equipment.

4.3.1 Duplexing

The equipment in all Direction Centers and Control Centers may be grouped into two general classifications: common and special-purpose. Common equipment is equipment critical to the operation of the Central; special- purpose equipment is vital only to a small fraction of the overall operations. The failure of common equipment would make the Central inoperative To avoid this, all common equipment is duplexed. Included in the common category are the Central Computer System, Drum System, Warning Light System, Output System, and some lesser elements.

Duplexing equipment makes it possible for one machine (called the standby machine) to be maintained in perfect condition without cessation in normal operations since its twin (called the active machine) is under. taking the processing of air defense data (fig. 4-1) Should a breakdown occur in the active machine, the standby machine takes over operations (thus becoming active), with the malfunctioning active machine now becoming the standby. The only delay encountered it this switchover would be met if the standby machine

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were undergoing corrective or scheduled maintenance. Such delay, however, would be very short.

In instances where the standby machine is operable when the active machine breaks down, no delay is encountered in switchover. Also, little or no information is lost, because the standby machine normally receives the same data as the active machine. (Figure 4-2 shows an outline of a typical, duplexed Central.) While the active computer is carrying out normal defense tasks, the standby computer runs a special program to store the data necessary to take over operations from the active computer. The standby computer also uses the program to check itself for optimum operating condition, to monitor the operation of the active computer, and to assist in the maintenance of equipment not in use.

Duplexing, therefore, is the arrangement whereby certain equipment is installed in duplicate to preclude the shutdown of the Central during correction of malfunction. Equipment that is not of such a critical nature - the failure of which would not render the Central inoperative-is known as simplex equipment No duplicates of these equipments are installed, as the Central is capable of operating without them.

4.3.2 Built-In Test Circuitry

Maintenance of the AN/FSQ-7 and the AN/FSQ-8 is accomplished by using maintenance programs with marginal checking.

Marginal checking (MC) is the method used to detect imminent circuit failures. The circuits are designed so that one or more of their associated supply voltage may be varied in prescribed amounts without causing circuit failure when the components are within accepted tolerances. Components outside of accepted tolerance require less voltage variation than normal to cause failure. Therefore, component deterioration can be detected by the amount of voltage variation required to cause failure. The voltage variation which causes circuit to fail is called the circuit margin. Marginal checking is not a maintenance tool, however, unless used with programs which operate the circuit to which the MC voltage excursions are applied.

The MC System serves to vary the MC voltages one at a time, over large sections of the system. For a more detailed reliability check, a breakdown of these large circuit groups is made on the expected circuit margins. A further breakdown is provided for the purposes of fault isolation in the event of a failure during a reliability test.

4.3.3 Special Test Equipment

Marginal checking of AN/FSQ-7 and AN/FSQ-8 equipment is supplemented by the use of special test equipment. Servicing, in this regard, encompasses the following maintenance activities:
  1. Repair of defective or marginal components removed during scheduled or nonscheduled maintenance of the Central
  2. Test of pluggable units, and components such as tubes, crystal diodes, and rectifiers
  3. Calibration and maintenance of test equipment

Test equipment is located in the maintenance and test area of the Central. Maintenance parts and special: tools are provided in the adjacent parts storage area.

To prevent power interruptions in the maintenance and test area from interfering with normal operation of the Central, the maintenance and test area is provided with its own independent power supply. This power supply provides power only for the special test equipment located at the Central.

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The AN/FSQ-7 Combat Direction Central and the AN/FSQ-8 Combat Control Central equipments are divided into both logical and physical divisions. The logical divisions are based on the operation of the system, such as the flow of information or intelligence through the equipment. With logical divisions, related systems, elements, sections, or circuits are grouped by operational functions. These groups carry the information or input through the equipment to arrive at a desired result or output. Physical divisions are based on the physical assembly of the equipment. Physically related component parts, pluggable units, modules, and units are examples of this type of division.

The organization of manuals for the AN/FSQ-7 and AN/FSQ-8 equipments is directly related to the divisions outlined above. Information concerning functional systems of the equipment can best be understood when compiled in manuals organized about logical divisions. On the other hand, installation, operation, maintenance parts listings (of physical groups), and special test equipment information can best be understood when compiled by physical divisions.

The manuals are structured to permit the reader to assimilate information in successively finer detail. Manuals not directly related to the equipment (theory) are organized to give the reader opportunity to stop at certain points in a manual and how the complete subject to a degree governed by the place at which he stops. This is possible because the divisions of the manuals are functionally complete and enable the reader to thoroughly understand the equipment, unit, element, etc. being discussed.


Manuals covering the various equipments which comprise or are associated with the AN/FSQ-7 and AN/ FSQ-8 Systems are divided into several distinct types, based on the area of discussion.

5.2.1 Theory Manuals

The purpose of the theory manuals is to discuss the AN/FSQ-7 and AN/FSQ-8 Systems as entities within themselves and to explain in detail the function, operation, and theory of their elements, sections, and circuits. Introduction Manual

This manual discusses briefly the SAGE System applications of the AN/FSQ-7 Combat Direction Central, applications of the AN/FSQ-8 Combat Control Central, and the major systems of the equipment. Theory of Programming Manual

This manual describes the flow and processing of information from a programmer's viewpoint. It explain instructions, indexing, coding, and the media of transferring information into and out of the equipment. Basic Circuits Manual

This manual describes the operation of the basic circuits employed in the equipment. Information circuits progress from the simpler to the more complex. Special Circuits Manual

This manual explains the theory of operation of special circuits that are peculiar to certain equipment areas. These circuits are known by various names, depending on their functions, and are presented in the manual in alphabetical order. Logic Index Handbook

This handbook is divided into seven major parts. corresponding to the logic designations of the six major systems of the AN/FSQ-7 and AN/FSQ-8, plus descriptions of duplex maintenance console and simplex maintenance console switches. Each part lists alphabetically by pluggable unit location, logic, and zone number the important circuits and pulses to be found in a system. In addition, there is an appendix "A", which presents a list of programming instructions and commands, and an appendix "B", which presents the programmer's data chart and color codes for equipment wiring.

5.2.2 Systems Manuals

The systems manuals present the theory of the systems (logical divisions) that comprise the AN/FSQ-7 and AN/FSQ-8. The systems are as follows:
a. Central Computer
b. Drum
c. Input
d. Output
e. Display
f. Power Supply
g. Marginal Checking

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Chapter 5, Page 40

Basically, each system manual is organized in the following manner. The logical function and theory of operation of the system is discussed in Part 1. The theory discussion is usually based on a simplified block diagram. The remaining parts of the manual are divided into the elements that make up the system. Each element is presented in a separate part and generally contains an introduction describing the equipment, a discussion of the role of the element in the system, and a detailed explanation of theory. The detailed theory of the element is based on logic diagrams.

If a further breakdown of the element is necessary, chapters are used and are also basically divided into general description and theory.

5.2.3 Maintenance Manuals

Twenty-one maintenance manuals, directly related to job assignments at each SAGE site, have been prepared. A different manual is provided for each working area in any given Direction Central or Control Central. The manuals are used in conjunction with a special card file, and the resultant manual-card-file combination ensures the correct, timely upkeep of all necessary equipment.

Each maintenance manual (except for the programming manual) is divided into seven sections:

a. Section 1 Introduction
b. Section 2 Preventive Maintenance Tasks
c. Section 3 Diagnostic Techniques
d. Section 4 Check Procedures
e. Section 5 Corrective Procedures
f. Section 6 Field Technical Instructions
g. Section 7 Miscellaneous

These manuals are supplied without lists of contents, illustrations, tables, indexes, and title pages. In short, they contain nothing that does not directly pertain to specific maintenance tasks. Each page, however, contains appropriate headings (in code) for rapid location of specific procedures called for either by the card file or by a reference note in some other part of the manual.

5.2.4 Illustrated Parts Breakdown

The illustrated parts breakdown (IPB) manuals contain a breakdown of the AN/FSQ-7 and AN/FSQ-8 equipment in the order of disassembly, with the supporting illustrations, descriptions, and other listings necessary for ordering replaceable parts. The breakdown does not go below the pluggable-unit level. The manuals are made up of an introduction, a group assembly parts list, a list of parts by manufacturer's part number, and a list of maintenance parts issued with the equipment.

5.2.5 Schematics Books

These manuals contain the logic diagrams, wiring diagrams, and other drawings associated with each system (Central Computer, Drum, etc.) in the AN/ FSQ-7 and AN/FSQ-8 equipment.

5.2.6 Special Test Equipment Manuals

The manuals for the various pieces of special test equipment in use at the sites are listed in the next portion of this chapter. Basically, these manuals are similar. Each manual contains theory, operation, maintenance, and an illustrated parts breakdown for the particular piece of equipment presented in the manual 5.3 ORGANIZATION OF MANUALS The manuals are organized as follows:
Theory Manuals
Theory of Operation - Central Computer System
Theory of Operation - Drum System
Theory of Operation - Input System
Theory of Operation - Display System
Theory of Operation - Output System
Theory of Operation - Power Supply System
Theory of Operation - Marginal Checking System
Theory of Programming
Reference Manuals
Special Circuits
Illustrated Parts Breakdown
Logic Index Handbook
Basic Circuits
Schematics Books
Central Computer System
Drum System
Input System
Output System
Display System
Power Supply and Marginal Checking Systems
Warning Lights System
Pluggable Units Books
Pluggable Units
Data Processing Manuals
Card Reader Type 713
Line Printer Type 718
Computer Entry Punch Type 020 -
Chapter 5, Page 41
Card Recorder Type 723
Tape Drive Type 728
Special Test Equipment
Test Set, Memory Driver Panel TS-986/FSQ
Test Set, Plug-In Unit TS-985/FSQ
Power Supply PP- 1589/FSQ
Test Set, Diode Semiconductor Device TS-990/FSQ
Test Set, Electron Tube TV- 11/FSQ
Adapter, Test MX-2 190/FSQ
Capacitor Reformer MX-2189/FSQ
Test Set, Plug-In Unit TS-1084/FSQ
Zener Diode Tester
Transistor Tester
Display Console Subassembly Tester
Light Gun Tester
Family Adapter
Maintenance Manuals
Air Conditioning System
Calibration (two volumes)
Card Reader, IBM Type 713
Card Recorder, IBM Type 723
Central Computer and Maintenance Consoles
Computer Entry Punch, IBM Type 020
Display Consoles (two volumes)
Display Generators, Manual Inputs and Warning Light Units
Drum System
Gap Filler Input System
Long Range Input and Crosstell Systems M1-12
Marginal Checking System
642 Memory
Output System
Photographic Recorder - Reproducer Element
Power System
Printer, IBM Type 718
Console Coordinator
Tape Power Supply System
Tape System
Test Pattern Generators


There are, in addition to the regular manuals described heretofore, other publications available to site personnel. These publications serve as sources of additional information, the specific nature of which is not covered in the manuals.

5.4.1 Instruction Bulletins

Instruction bulletins (IB's) are designed to provide up-to- date information to authorized site personnel as soon as the information becomes available. In certain cases, IB's supersede applicable portions of particular manuals until such time as the information is included in the manual by revision. In most instances, however, IB's cover areas of pertinent information which do not come within the scope of the regular manuals.

5.4.2 Program Library

Each site has a file known as the program library, which contains primarily listings of maintenance programs although virtually every type of program used at the site is also listed. Programs are filed according to preassigned index numbers. The material to be found in the library consists of program writeups, program supplements, program listings, and the media (cards or tapes) by which the programs are fed into the equipment.

5.4.3 Military Reference Data Books

Complete sets of military reference data (MRD) books are furnished to each site. In these books are details concerning standards and specifications to be adhered to in the various phases of manufacture and repair. There are two major areas of application which would be of particular interest to site personnel. Electrical Standards

This area provides standards and specifications dealing with electrical, electronics, and logic standards; electrical components standards, electrical drafting standards, and electrical specifications. Mechanical Standards

This section presents mechanical standards, mechanical drafting standards, manufacturing (plating, soldering, for example) specifications, and mechanical components.

Chapter 4, Page 42

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Subject Page Figure Side
Air defense problem 3 - 2.1
AN/FSQ-7 and AN/FSQ-8:
definition of
1 - 1.1
description of
11 - 3.1
information flow
12 3-1 -
11 - 3.2
Arithmetic element 19 -
Built-in test circuitry 36 - 4.3.2
Cape Cod System:
3 - 2.3.1
3 - 2.3.2
Central Computer System 17 - 3.2.3
Combat Control Center 7 - 2.4.2
Combat Control Central 11 - 3.1.2
Combat Direction Center 4 - 2.4.1
Combat Direction Central 11 - 3.1.1
Combined Direction Center-Control Center, physical description 25 - 3.3.3
Communication between operating personnel and equipment,
major means of
9 2-4 -
Computer and auxiliary devices 18 3-5 -
23 3-8 -
22 3-7 -
duplex maintenance
19 -
duplex switching
19 -
simplex maintenance
14 -
Continental Air Defense System 3 - 2.3
Control Center:
floor plans
31 3-13 -
functions of
7 - 2.4.2
physical description
25 - 3.3.2
Crosstell element 14 -
Detection 4 -
Direction Center and power building 31 3-12 -
facility requirements
26 3-10 -
floor plans
27 3-11 -
4 - 2.4.1
physical description
25 - 3.3.1
Direction Center-Control Center and power building 33 3-14 -
Display console facilities 22 3-7 -
Display System: and display drums 21 3-6 -
20 - 3.2.4
Displays and associated equipment 22 -
20 -
20 -
Division, information flow 8 2-3 -
Drum System:
14 - 3.2.2
OD and CD sides of
16 3-4 -
operational block diagram
15 3-3 -
17 -
16 -
Duplex Central, outline of 37 4-2 -
Duplex maintenance console 19 -
Duplex switching console 19 -
35 - 4.3.1
typical arrangement
36 4-1 -
Equipment approach to maintenance 35 - 4.3
Experimental SAGE subsector 3 - 2.3.3
Former system and its limitations 3 - 2.2
Gap-filler input element 12 -
Identification 5 -
Input-output devices 19 -
Input System: and input buffer drum 13 3-3 -
12 - 3.2.1
Instruction control element 18 -
Instruction bulletins 41 - 5.4.1
Internal storage devices 19 -
Long-range radar input element 14 -
console, simplex and duplex
19 -
equipment approach to
35 - 4.3
35 - 4.2
Basic Circuits
39 -
39 -
Logic Index Handbook
39 -
Special Circuits
39 -
Theory of Programming
39 -
Manual controls and computer indicators 19 -
Manual data input element 14 -
illustrated parts breakdown
40 - 5.2.4
40 - 5.2.3
organization of
40 - 5.3
philosophy of organization
39 - 5.1
schematics books
40 - 5.2.5
special test equipment
40 - 5.2.6
39 - 5.2.2
39 - 5.2.1
types of
39 - 5.2
Marginal checking 36 - 4.3.2
Messages, output 23 -
Military Reference Data books 41 - 5.4.3
Output control element 24 -
Output messages 23 -
Output storage element 24 -
Output System:
block diagram
24 3-9 -
23 - 3.2.5
Physical description of Centers 25 - 3.3
Power building for combined Direction Center-Control Center 34 3-15 -
Program control element 19 -
Program library 41 - 5.4.2
Purpose of manual 1 - 1.1
Reference materials:
Instruction Bulletins 41 - 5.4.1
Military Reference Data books 41 - 5.4.3
program library 41 - 5.4.2
Reliability defined 35 - 4.1.5
description of
4 - 2.4
experimental subsector
3 - 2.3.3
relationship to the Air Defense System
5 2-1 -
Scope of manual 1 - 1.2
Sector, information flow 6 2-2 -
Selection control element 18 -
Simplex maintenance console 14 -
Special test equipment 36 - 4.3.3
41 -
41 -
Storage devices, internal 19 -
System breakdown 11 - 3.3
Test circuitry, built-in 36 - 4.3.2
Test equipment; special 36 - 4.3.3
Test pattern generator14 -
Weapons control 5 -