CIA HISTORICAL REVIEW PROGRAM
TITLB: The Yo-Yo Story:An Blectronice Analysis Case History
AUTHOR: Charles R. Ahern
VOLUME: YEAR: 1
STUDIES IN
INTELLIGENCE
A collccllon ol orticlos on the historical, operational, doctrinal, and Iheotetlcal aspects ol intelligence.
All siaiemenis of faci. opinion or analysis expressed in Studies in Intelligence are those of
ihe authors They do not necessarily reflect official positions or views of the Central Intelligence Agency or any other US Government entity, past or present. Nothing in the contents should be consirucd as asserting ot implying US Government endorsement of an article's factual statements and interpretaiions
Exemplary but unusual history of the detectionovietsystem.
THE TO-ro STORY: An Electronics Analysis Case History
Electronic componentsritical part of modernsystems, less dispensable than some of their more obviously Important features. It is possible to conceive of sn airsystem without interceptor aircraft, for example, but it is not possible to conceive of one without electronic devices, systems, and techniques. Intelligence on the electronicof Soviet weapons systems has therefore become a. key Item in our knowledge of these systems. Herease history uf community teamwork In gaining such Intelligence on antype ot radar control for surface-to-air missiles in the Soviet air defense system. The story features aeffort to obtain observations, an Imaginativeucky break, and an excellent follow-through by research and development.
Herringbones and Ventilators
In the. and British Intelligenceookout for signs of the Soviet deployment of surface-to-air missiles in readiness for defense against air attack. Toward the end3 some unusual road networks were seenof Moscow, which, although they did not have theconfiguration of missile sites, were at least located at points where missile Installations might be expected. As the pattern of these locations began toore intense search for them was made. By the autumn4umber of reports consistently described the networks asthree more or less parallelile longby some ten cross roadsalf mile In lengtherringbone pattern. There was nothing In the reports that would particularly excite the curiosity of the specialist InIntelligence.
During the last quarter of thatnd UK attaches began to report details of other features around thecomplexes In the Moscow area. Inritish observer, without making specific reference to It In the body of his report, Indicatedketch that therebarracks area" some distance away, more or less In line with the sods of the herringbone and connected with itoad.ouple of weeks this report was amplifiedifferentbarracks area located. The original "barracks."to the revised description, seemed toongbunkeroncrete hand-stand at one end. The observer noted that large ventilators at this end of the bunker flapped with what seemed extraordinary violence, even when the fairly high wind blowing at the time was taken Into
A week later, when. attachesalf hour out from Moscowlane bound for Leningrad, one of them noticed an unusual Installation on the ground. Itook of newness and activity about It. He didntery clear impression of any buildings on the site; his eye was caught by the motion of two large wheels Installeditamp leading down to them. Each wheel, he reported, washinith twin flat disks spinning at an angle to tbe horizontal. He estimated their speed at aboutpm and said they appeared to wobble on their axes. He had difficulty describing the nature of this wobble; It appeared toind of "even undulation throwing the outside edges [of theoot or two from their planes ofis sketch is shown in Figure 2.
This report proved toemarkably accuratethe device thereupon nicknamed the Yo-Yq.1the observer had only five or ten seconds to take toof something never before seen or beard of. Hison the flight, seated on the other aide of theIn the course of the trip spotted one of theand when he returned toew days laterIt In response to the standing order forthese. When the two men checked their observationthat the Yo-Yo and the herringbone hadbe^^nnccCion
between them. They astutely guessed that the Yo-Yosome kind of missile guidance system, and thisIn tbe report brought it to the attention of
A month later, about the beginning of December. British observers ridingrain southeast of Moscowenced areaicrowave antennaole at one-end. In the center of the enclosure there was an earth bunker with one open end facing the pole. There theydoublediskach disk, they Judged, about ten feet In diameter and makingevolutions per minute. The plane of the disks was inclined at aboutegrees from the horizontal. The observers had the impression that the disks either had serrated edges or were polygonal structuresisk-like appearance by tbe rotation.
In5 this same site was observed. personnel. Their photography was notcale or quality to convey any clear Idea of the shape of tbe Yo-Yo, but their observations, erroneous In part, did correct and refine some of the earlier Information. They reported that the two disks were each abouteet In diameter and aboutnches thick. They thought them both vertical, at right angles to each other. They were not sure whether they were double, and If so whether the two halves rotated in the same or opposite directions. They estimated the rotation to
'BoTlrt Bloc electronics Items are assigned ntcJnumsf. as opposed to code Dames or cover names, toommon pomenclatare In the collet Hon and production of Intelligence. These nlcanamea are selected and agreed uponripartite basis among electronics Intelligence represcntaUvca of the United States, the UK, and Canada.
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stages-- pfaWt v. -
Tht Yo-Yo Slory
l bou^4o'rpm ana stated that there was no wobble, anIllusion of one being given by the viewing angle and the serrated edges.ketch supplied with this report.
At this stage it was by no means clear that the herrwgbone complexes had anything to do with missiles. No missile had been seen on the sites, and the road arrangement would have been equally suitable to housing development or crop or anv ra unit ton storage. Even If they were surface-to-air missile sites. It was not firmly established that the Yo-Yo was uniquely related to them. Further, there was nothing about the Yo-Yo to indicate that it was an electronic device; the reports on It did not even convey any clear idea of what It looked like. One offhand opinion received from British experts was that It mightock crusher.
Nevertheless, under the good-humored assumptiono one can figure out what It Is, It must behe Yo-Yo reports were laid before tbe Joint gatherings ofelectronics specialists at that time sponsored by the old Military Electronics Working Qroup. Beginninghe Yo-Yo was brought up at each meeting of the MEWO for many months. For tbe present, however, there was little that the electronics analyst could do but speculate as to what the observers had really seen and request more detailed Information, especially photographs.
By tbe summer5 It bad become more or less clear that the Yo-Yo didpecific relationship to tbecomplexes. The herringbones were arranged so that their length was alwaysadial line from Moscow. Tbe Yo-Yo bunker was situated on this same line, centered on tbe herringbone, and alwaysile nearer to Moscow. Tbe
Yo-Yo Itself was invariably at the herringbone end of the bunker. But the true shape and appearance of the Yo-Youncertain.
Early Inacket of photographs was brought to CIA electronics analysts.o-Yo southeast of Moscow, they had been taken, happily, from several different angles. These photographs revealed, at last, what the Yo-Yo really looked like. The observers had for the past year been more or less correctly and accurately describing what they
Star of David configuration. There were two such assemblies, one ln the vertical Moscow-herringbone plane and the other (of which an edge is visible In the accompanyingat right angles tilting upegrees from the horizontal toward the herringbone. The early "violent flapping of the ventilators" and wobbling wheels were now. comprehensible optical Interpretations of the two assemblies in rotation.
Analysts and
The analyst, as Is usually the case In electronicsthus found himself confrontedully developed Soviet device deployed In the field. In these circumstances his task is one of unravelling what the Soviet designer was
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attempting to achieve, the reverse ot the original designWhereas the Soviet designer Iset of performance specifications and proceeds by selecting available techniques, components, and production processes and by making thetechnical compromises to reach his final design, the analyst must work backward from the finished design toat the designer's objective. In this process he must also take care that his thinking Is not controlled by concepts of how an Item would be designed in the United States: the So-
In the absence of any similar, previously known piece of equipment from which to extrapolate, the analysis of the Yo-Yo problem had to beginasic assumption as to the general purpose of theIt was designed to control surfacc-to-alr missiles launched from the herringbone srea (though no missiles had yet beenranted this assumption, the problem became that of figuring out howcould be guided by an apparatus with such anas that shown in the photos and the placement anddescribed in the observer reports. The analytic point of departure was the consideration that, however tbe Yo-Yo worked to guide the assumed missiles, it would have to provide Information with sufficient accuracy on both the missile'sand the missile itself In threeand azimuth.
In virtually all surface-to-air missile guidance systems this tracking of the missile and Its target is doneystem of radar antennas, say of parabolic form, that point towardand target and focus beams of radio energy on them, muchearchlight does with its visible beam. Before the Yo-Yo photos were received the possibility could not be ruled out that it too wasarge parabolic reflector Imperfectly observed and poorly described; but the form shown in the photos was clearly no conventional variety of antennaAll the available descriptive Information indicated that the Yo-Yo disks retained their relative position whileThis meant that only the edges of the disks could point upward and away from Moscow, the direction in which radar antennas should be looking for enemy aircraft and should guide missiles to attack them. The straight sections of these
edges seemed the most likely portion for antenna apertures. This reasoning provided the germolution.
The straight sections were abouteet long andInches wide. An aperture of these proportions could betoransverse fan beam aboutimesIn the plane of Its short dimension as in that ofGiven the orientation, arrangement, andof the disks, it appeared that on each rotation ofassembly six of these narrow beams, one from.traight edge..would scaniabeyond the herringbone complexes. The size andof the apertures had apparently been one of theon the mechanical designer: since six would havehuge, unwieldy single disk, he had divided them between two
f-David triangles.
The six beams from the tilted Yo-Yo would thus scanapproaches to Moscow In azimuth and those from the ver-
tical assembly would scan It in elevation. Both sets could provide range data on any target or missile In the volume of space scanned. With the whole volume covered, the antennas would not need,earchlight or parabolic radar, to stop scanning in order toarget or the defense missile, but would provide position data on these in the course of continued scanning. Inystem, therefore calledemory devices would be needed to develop the track by maintaining continuity of information during thebetween the individual antenna scans. Such devices were considered possible.
A series of calculations, based on guided missile performance requirements as well as radar needs, were then undertaken. Guided missile analysts furnished estimates of the probable range of Soviet surface-to-air missiles and the size of their warheads. The former provided limits for certain technical characteristics affecting the range requirement of the radar; the latter helped define Its accuracy requirements. In all, two dozen or more technical factors entered the calculations. These had to be weighed against one another In reaching the compromises that are always forced upon the system designer:
dimensions of the beam are Inversely proportional to those of the aperture that produces It
for example. if the operating frequency were too low, accuracy would be poor and transmitter power requirements excessive; if it were too high, the rapid scanning rate of the antennas and the narrowness of the beams would make too few pulses hit the target.
As the designissile guidance system evolved from thisheck was made with analysts In the field of vacuum tubes and other electronic components to Insure that it did not call for techniques or components beyond .Soviet,
lshed^ha^ox^ffito' operating principle of itsthe technical characteristics of the radar, the accuracy of the system, and its anticipated capabilities..
One taskre-examine the "entire solution against any possible alternatives in the light of all reports and photographs, mquiring whether everything reported could be accounted for In the solution and whether anything required by the solution and not reported would seriously weaken it. Each alternative solution that came to mind failed to account for some aspect of the reported data orapability on the part of Soviet technology that appeared unreasonable. One suggestion, for example, was that the Yo-Yo antennas would simply radiate energy to Illuminate the targetoming system In the missile.ystem might work, but because of the discontinuous nature of the radar signal It would require the inclusion of memory devices In thegear of each missile. This elaborate provision seemedFurthermore, the homing Illumination theory was Inconsistent with the configuration of theingle pair of disks should give adequate illumination, so the two at right angles to each other would be an unnecessary
Testing the tentative answerroblemairlyprocedure, but testing this answerarticularlytask because of Its startling implications. If it was right, the Soviets had not continued In the direction taken by the original German wartime development ot surface-to-air missile guidance nor in that of postwar Western efforts, which were based on extensions of the German work. Instead,lean break with precedent, they had arrivedesign that was Inherently capable of dealing with multiple
'
Yo-Yo Story
targets simultaneously. The data on the target or targets were apparently translated automatically Into rnlssUrguidance: there were no Indicationsoming system on the missile.
This analysis, which required some three weeks from the time the photos were received, was made the basis for aScientific Intelligence Report Incorporating itsandist of probable technicalhe pubUcatlonjjf the report.wouldtjltft- #kW*-" endRJbuttory*MnlqueT"For one
thing, the report found, with Its unprecedentedby no means unanimous Initial acceptance among theof the Intelligence community concerned withand guided missiles. For another. It was brought in
eries of steps initiated by Army intelligence, before the Technical Advisory Committee onof the Assistant Secretary of Defense for Research and Development, and the Committee recommendedroject be Initiated torototype or mock-up of the Yo-Yo as therein conceived. The mock-up technique, used during World War II. had led to an assessment of theof the German radars and was Invaluable in developing electronic countermcasures to foil them, but its use had not been common in the decade following the war.
Int about the same time It became fairly well established that missiles were actually era placed on the herringbone complexes, the mock-up contract was let through Army Ordnance and work on It begun.
trpkfitationreak
M can while the Dragon Returnee Program had beenon repatriated Perm an scientists and technicians who had been taken to. after the war. Many of these gave Information of some value to electronics and guided missile intelligence, but it appeared that the Soviets had carefully kept the German electronics specialists Insulated fromwork in military electronics, especially in the heavy radar field, where the results of Soviet efforts wereIncreasingly evident from other sources. After sev-
'PTOvUlOQal Sdenuflc InUUurence Report,ossible Sonet Missile Ouldance System."
era! years of experience with returnees, the chances ofone who knew about the development of specific highelectronics Items were privately Judged at about one in ten thousand.
In the fallear after the publication of the Yo-Yo analysis, one of the Dragon returnees, Christian Sorgc, who it was thought might have Information on amissile system, called attention during his routinedebriefingew development on which he had
looking antenna system, which he then sketchedheet of paper for the interrogator. The Interrogator, looking at
Figureoise's Sketchntenna
the superimposed equilateral triangles Sorge had drawn,the published Yo-Yo analysis and realized withexcitement that Sorge had knowledge more Important than had been supposed. As the preliminary debriefingthe Identity ofith the analyticof the Yo-Yo was established at some dozen points.
The intelligence community noweam ofto assist in Sorge's debriefing. Their efforts brought out more and more technical details, especially of the memory portion of the. system, the complex electronic trackingmade necessary by the adoptionuidance system dependent on the discontinuous data of scanning antennas. It was this critical part ofystem, fortunately, that Sorge had worked on. By the time his debriefing had
The Vo-ro Sfory
been completed he had provided many new Insights, as well as having confirmed someracts hypothesized In the analytic reconstruction. One curious reaction to the Initial correlation between the analytic report of5 and Sorge's Information had been the suspicion that the report might have fallen into KGB hands, who through Sorge were now feeding it back to the Interrogator, This fear was quickly dispelled by the amount of detail and consistency in Sorge's data.
ad been assigned tasks onystem, which had apparently been conceivedn addition to the details of circuit designs, he described some of the testing programs for the prototype that begannd hiswas supplemented by that from some of the others who had returned. But2 they had all been removedevelopment and placed In non-sensitive activitiesoollng-off period of three or four years prior to repatriation.
FoIZoi^rnrouj/ri
The group of specialists assisting in the debriefing of Sorge included personnel from the Diamond Ordnance Fuzethe contractor for the Yo-Yo mock-up project. Asof the tracking system and other portions ofere brought out by Interrogation, they were promptlyin the development work, effecting important changes in Its direction.ajor example, although the analytic report hadeparate computer for eachengagement, the DOFL people had decided that the Soviets wouldingle large digital computer, Sorge's statement that separate analog computers were In fact called for In the design now broughtimely reorientation in the mock-up project. It was fortunate that the project was already contracted for and under way when Sorge appeared: atear and perhaps more was saved by having ateam assembled and working on the problem before being overwhelmed byolume of detailed Information.
As It was, the development project, begun inid notrototype Installation that could be tested until early The results of tbe test program showed the
oajor technological advance In radar tracking systems. An additional surprise was that It performed much better than expected when tested against electronic counte measures. Jamming; but the technique of dropping chaff was effective against It If properly employedas found to have an angle accuracy as greatn strong targetsange accuracy ofards; this meant that missiles in the range ofoiles would notoming radar of their own. Its low-altitude capa-
The ability of the system to cope with multiple targets was confirmed; the ability of one Installation to direct as many asrimultaneous target-missile interceptions, as claimed by the Germans, seems to depend only on whether the Soviets choose to provide the necessary computer for each Interception.
Thus the Yo-Yo story, which began with the reportsew alert observers who noticed some unusual Installations3nds with the tests of the mock-up system In the autumnt raises some interesting questions, for example how quickly the Sorge information would have been believed if the Yo-Yo sites not been seen, reported, and analyzed. Even with the analytic report in hand, some of the specialists Involved In the debriefing doubted much of what Sorge said in the early stages. The approach of the analytic report itself, the setting out toovietronlc system on the basis of its physical appearance, was unique; It succeeded hugely because the design was sofrom anything theretofore developed.
The concern of electronics analysts about the new Soviet guidance system has remained undiminished, because ouron its internal workings ends witheriod, and what the Soviets may have done In theyears to improve its performanceontinuing problem-Several studies have considered what Improvements could be made in. but no intelligence Information has come to light on any that nope been made. And now the recent appearanceecond-gene ration missile guidance system, Fruit Set. which might be loosely describedobile Yo-Yo, is tending to push thento the background.
Original document.
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