Shough Report

1. Abstract

2. General Description of the Radarscope Photographs

3. Frame-by-Frame Description of Radarscope Photographs

4. Radar Specifications and Mode of Operation

5. Reconciling Time and Distance Data

6. Interpreting the Unidentified Echoes

7. Conclusions



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Anomalous Echoes Captured by a B-52 Airborne Radarscope Camera

Martin L. Shough

5. Reconciling Time and Distance Data

Knowledge of the positions and altitudes of the B-52 at the times when the radarscope photos were taken is important, both for interpreting the display indications and for the overall coherence of a reconstruction of events. The clock, the frame counter, and a timeflagged transcript of RAPCON radio communications, together hold out the promise of precisely cross-correlated events in this case. There are some unexpected problems with this, however, and it becomes important to be able to check the consistency of our reconstruction against internal evidence recovered from the radarscope photos.

Firstly let us consider the solitary sector scan which we have tentatively identified as frame 784 and where the radar system status is encoded in an array or "plaque" of 6 data lamps as shown in Fig. 5, Section 3. It is possible to verify that the pattern of lamps on frame 784 fits only one configuration of this array, identifying the following mode of the radar:

graphic from shough analysis

The function of the Deadman Switch is uncertain. The scan direction indicates that the camera was triggered at the end of the counter-clockwise trace rotation. The Memory Point is not discussed in available documents, but presumably this is the PDI or Position Direction Indication that McCaslin recalled using to fix the UFO "landing" point so that the navigation computer could automatically bring them back to overfly it after their first go-around at Minot (although in fact the go-around could not have taken the B-52 within several miles of this location). The Memory Point is "off" here as a default, but is engaged by the navigator depressing a single switch.

The 20 NM range scale makes the radius to the edge of the first ground return more than 5 NM. But given the known altitude of the descending B-52 as at frame 783 (see Section 5-2) this is hard to understand in terms of any listed mode of the radar. It is also disquieting that the radius of the hole as seen on the tube appears almost identical to the altitude hole radius on frame 783, an uncomfortable coincidence given a changed range scale.

It has been suggested that the navigator switched the radar into Indirect Bomb Damage Assessment (IBDA) mode to scan aft of the B-52 when the target vanished. This makes practical sense, and switching to IBDA mode would enforce the change from 5 NM to a longer range scale (for the obvious reason that bombing altitude is over 20,000 ft) ; but this automated mode enforces an off-centre sector scan ahead of the aircraft when first entered, which then changes to a full PPI scan at 20 NM, and not a sector scan, after bomb drop. Terrain Clearance mode also enforces a sector scan ahead of the aircraft, for obvious reasons. (The hypothesis that frame 784 should be inverted, showing a forward sector scan 24 degrees either side of an a/c heading of about 308 degrees, was rejected because the camera data lamps then become unintelligible.)

In a recent interview, Richard Clark, the Bomb Wing intelligence photoanalyst who originally had the set of prints made in 1968, recalled that this sector scan photo probably preceded frame 771. This implies the possibility that it shows a Ground Map mode entered near the start of the incident when the plane was at higher altitude (near 20,000 ft MSL). In this mode the display is altitude-compensated so that the >5 NM radius to the edge of the first ground echo is not slant range, but true ground range from the nadir to the heel of the beam. But according to CDC 32150K, Vol.4 this radius is automatically kept at 3NM in this mode, not >5 NM, and the coincidence of the similarity between the measurements of the actual 783 and 784 PPI images remains uncomfortable.

In the end it is impossible to definitely identify the radar mode in this sector scan frame or to be certain when it was taken so it is of little help to us. Fortunately, for the remaining 13 frames the radar mode not is in doubt, allowing us to extract useful information. This may help to remove or reduce ambiguities in the reconstruction of events that documents and witness statements are unable to remove.

As mentioned earlier it appears that we have only around one tenth of the radarscope photos originally taken. Richard Clark, the 5th Bomb Wing Intelligence Officer who examined the original negative film in 1968 and personally ordered the prints made, recalled that there were probably "over a hundred" frames in addition to the 14 (including the anomalous frame #784) that he ordered printed up. This total could be consistent with the camera having been switched on close to the beginning of the incident (38 NM out according to the official file) and left running through to the end of the incident about 14 NM from Minot runway, which would have generated in the region of 120 frames in total.

According to Clark's recollection, the 13 consecutive frames 771-783 came from the beginning of the negative strip, and the sequence 771-773 records the initial high-speed approach (as it was construed) of an unknown target and its motion from the right to the left of the scope where it began to keep station on the B-52. In general, the positions of the echoes on the photos appear to be somewhat similar to the way this behaviour is characterised in the earliest official report. But at the same time there is contemporaneous documentary evidence suggesting that the photos were taken near the end of the incident, and also the match between the above scenario and the photographed target kinematics is not without anomalies, in particular, consistent evidence that the initial right-to-left transit by the echo occurred during a wide radius turn near the TACAN approach beacon. The photographed heading marker shows no evidence of a turn. So questions remain. The first question to address is whether the scope photos reveal any internal evidence of the map location of the aircraft.

Attempts to investigate this issue have been made by the twin routes of i) matching ground echo features against topographical maps of the area, and ii) determining the aircraft altitude from the photos for comparison with known elements of the approach path. The results of i) are inconclusive (excepting some recent work by Claude Poher discussed below), and the results of ii) invite real doubt that the extant photos can have been taken at or near the beginning of the UFO episode.

5-1. Ground Features

Attempts to correlate some apparent ground echo features with local topography were begun by Jim Klotz. This work will not be discussed here. The present section is limited to describing a few apparent ground echo features which should probably be excluded from the mapping attempt. Investigation suggests they are blemishes of some kind.

Feature #1: This feature is visible on all scans as a dark mark against the speckles of noise or ground clutter just inside the 1.75-mile range ring at ~92 degrees azimuth. Early impressions were that this was a lake. Bodies of calm water tend to specularly reflect radar energy away from the antenna, unlike rougher ground textures which scatter energy back to the antenna, and do appear as "negative" returns against bright ground echo. However close inspection reveals anomalies.

Firstly, measurement of the indicated bearings shows that the feature does not fall aft of the B-52 heading as would be expected, indeed it advances a degree or two in the direction of flight; secondly on frame 777 the same dark mark can be seen partially occulting a bright blip (a possible unidentified echo, but appearing only for one scan) with a fairly hard edge, in such a way as to suggest an obstruction either on the glass or near the camera film plane; and thirdly, and most importantly, a similar mark appears on frame 771 in the same position, even though this is in the half of the radarscope that has yet to be written on, the first complete sweep rotation having not reached that part of the tube (see Fig. 6 below).

Graphic from Shough analysis

Fig. 6. Details of Feature #1 from frames 771 and 777.

Features #2 & #3: These are two small dark features in the bright ground echo behind the plane, at first glance resembling negative returns from small lakes or ponds, of which there are many in the area (see Fig. 7 below). However to check this resemblance all the displayed ranges to the most distinct of the pair (Feature #3, @ ~312 degrees) were remeasured as closely as was practical. The results are tabulated below.

graphic from shough analysis

Table 1. Radial distances in mm from the inner edge of Feature #3 to the outer edge of the centre spot and to the edge of the altitude hole. (An effort was made to estimate the nearest mm; however the edges are blurred, so there is some uncertainty. Measurements were made with a steel rule on the computer screen, with each image in the same position on the screen to eliminate possible distortion.)

Evidently the distance from the "lake" to the edge of the altitude hole increases over time (the hole shrinks inward from ~2.1 miles radius to ~1.8 miles, presumably because the plane is descending whilst the vertical coverage angle stays fixed) as one might expect. But the distance from the centre spot fairly systematically decreases even though the aircraft heading (132 degrees) is almost precisely opposite the bearing to the "lake" (~ 311-312 degrees, this hardly changes detectably). In other words the slant range to the "lake" aft of the aircraft actually decreases by about 428 ft in 33 seconds, or it exhibits a closure rate of 778 ft/min = roughly 8 knots.

graphic from shough analysis

Fig. 7. Detail of Features #2 and #3 from frame 772

Obviously the slant distance to a stationary lake should change like the vector sum of the plane's forward motion and its rate of descent. The contribution of the descent will indeed be negative, but very small compared with the positive forward velocity (~250 mph), for any angle of descent smaller than about 45 degrees or so, even at the highest possible altitude of the B-52 (20,000' MSL), and reduces rapidly at lower altitudes. The real situation - deduced from the photos, the equipment characteristics and the probable approach path (see below) - appears to be that the aicraft's angle of descent and altitude are around 1/10 and 1/2 respectively of the above values, so we conclude that ground features could not reduce in displayed range as do Features #2 and #3.

If the measured displacement of the objects is not consistent with ground features, the question remains as to why they do change apparent position at all. This remains unexplained. The unlikely hypothesis that they are flying objects with efficient stealth characteristics (see also Section 6-2 ), appearing as "holes" in the bright ground echo, was considered but rejected after close examination of frame 771. As was found in the case of Feature #1, a small dark mark can be faintly discerned in the position of Feature #3 at ~312 degrees, again in the part of screen on which the rotating trace has not yet written. This appears to prove that Feature #3 is an artefact of a similar kind. (The same test is inconclusive in respect of the fainter Feature #2.)

Graphic from Shough analysis

Fig. 8. Detail of feature #4 on frame 771. The vertical striation crosses the bearing ring and extends beyond the edge of the PPI.

Feature #4: Another class of markings will be collectively named Feature #4. As in other cases, the same or a very similar feature is found on a number of frames, particularly 771, 776, 779, 781, 782 and 783, a relatively bright line generally running vertically from about 90 degrees to about 328 degrees with very small variation. It has been suggested that this indicates a highway. However close examination shows that a faint continuation of this feature can be traced extending beyond the tube face in some instances, crossing the bearing ring and onto the instrument fascia as shown in Fig. 8 below. On certain frames parts of the feature resolve under magnification into what appears to be a complex of tiny abrasions. The approximate position on the negative appears to be the same in most cases, and the orientation aligns parallel to the edge of the negative strip.

One inference would be that the original film roll was scratched at some stage, possibly in the camera feed mechanism or when when being spooled through the viewer at Minot. But the positive print image of such a scratch ought to be dark, of course, not bright, unless the prints were made from an intermediate contact film positive which was itself damaged in this way, in which case the prints would be negative images. They are not. If there was no interpositive film stage in the production of the prints then we are left with scratches on the enlarger slide or the glass of the print frame, which both seem very unlikely since the marks would then have the same appearance in roughly the same position on all photos, and they don't. So how these apparent abrasions got there remains a small mystery.

Several promising ground features are removed from consideration by this analysis, leaving one convincingly lake- or river-like serpentine feature on frame 783 as almost the sole point of reference for a topographical match. The likelihood that this will prove sufficient to fix the aircraft location appears small, but in combination with a second approach it might still be valuable. We turn to this next in Section 5-2.

ADDENDUM: A recent computer analysis by Claude Poher has indicated a pixel-level correlation between a part of this frame 783 feature and a part of the W shoreline of Lake Darling. If this is reliable then it places the B-52 about 5 nautical miles or more back from any position indicated in the contemporaneous documents (including the Base Dispatcher's concurrent log of events, Col.Werlich's chart of the flight track, TACAN coordinates entered in the AFR 80-17 report, and the copilot's report of position in the RAPCON transcript). There is no clear explanation of this discrepancy. Nevertheless, the figures given in the case documents are themselves not entirely coherent and attempts to find a different topographical match for frame 783 have not so far met with success. Lake Darling appears to be the only feasible candidate less than 5NM (PPI slant range) from the flight track.

5-2. Aircraft altitude

Measurements of the radarscope images were interpreted with reference to characteristics of the radar to indicate limits on the possible flight altitude. The results of such an investigation provide quite strong evidence that the altitude of the aircraft is grossly inconsistent with the known altitude at the time the first echoes were reportedly detected.

This tends to support the 1968 reconstruction of the incident by Col. Werlich in which these extant photos were taken at or near the end of the incident (some 19-16 statute miles, or 16.5 - 14 NM, from the runway according to his contemporary record).

Accurate altitude determination by this method depends on knowing the depression angle of the bottom edge of the radar beam where it intersects the ground. If we know the depression angle we can calculate the altitude from the displayed slant range. This angle depends on two variables: The tilt angle of the antenna boresight, and the vertical coverage pattern of the beam which is itself a fairly complicated function of range due to the cosec^2 vertical profile (the aircraft orientation is immaterial since the antenna tilt is servo-stabilised by pitch and roll signals from the ASQ-38 computer). Even a simple pencil beam does not have a definite edge, of course; rather the edge is some nominal contour defined in terms of power density, resolution or probability of detection. But in the present case the "edge" has a rather clear operational definition, as that vertical angle from the antenna boresight corresponding to the fairly sharp transition between altitude hole and ground echo on the PPI.

Graphic from Shough analysis

Fig. 9. Schematic diagram of vertical coverage and aircraft altitude In modes designed to scan the terrain (B) the radar operates with the beam depressed, the conical "altitude hole" below the aircraft shrinks to a vertical angle of a few degrees and the PPI shows an altitude-compensated map of true ground range. In Station Keep mode (A) the beam is elevated to detect airborne targets, the altitude hole widens to a cone 76 degrees wide and the PPI shows uncompensated slant range like an ordinary surveillance radar.

The relation between vertical coverage, displayed range and altitude (see Fig. 9) is simplified by the fact that there is no altitude compensation in Station Keep and the displayed range is simple slant range. This being so the depression angle of the bottom edge of the beam below horizontal is the key to the trigonometry. Training manual CDC 32150K, Vol.4 and the HSBR/IHSBR/ACR Tech Order together indicate that a) the vertical beam angle varies from 54-60 degrees; b) the angle widens as the antenna is elevated; c) in station keep the antenna is maximally elevated; therefore d) the angle in station keep is probably 60 degrees; e) the training manual gives the top edge beam angle as +8 degrees, therefore f) the depression angle is about 52 degrees. [Since it is not certain that b) continues to apply when the radar is in Station Keep, it is possible that the depression angle is about 46 degrees. For the moment we continue to assume the former value, but for certain purposes it will be sufficient to adopt a representative value of ~ 50 degrees.] Slant range varies like the sine of this angle and so we can calculate an approximate aircraft altitude.

We can also cross-check this against another inferrable quantity, the rate of descent. The true rate cannot be known independently of the true altitudes, but we can use the fact that the altitude hole radius reduces from about 2.1 miles to about 1.8 miles in 36 seconds to calculate some limits and a set of values for a range of radar angles. Since the B-52 was performing a text-book approach to the Minot AFB runway from a known altitude on a pilot evaluation exercise, the various descent slopes consistent with the photo sequence can then be compared against expectation based on two other known data - the average angle of the entire descent from the moment of leaving FL 200 and commencing approach, and the slope of the final glide path printed on the Minot approach plates.

All else being equal (i.e. if the computer-compensated antenna tilt stays the same, as seems to be the case as there are no discontinuous jumps in the size of the altitude hole) then the slant range from the antenna to the ground (altitude hole radius) is decreasing at the average rate of ~3080 ft/min during the 36-second photo sequence. Obviously the rate of vertical descent is less than this. The true rate would vary as the sine of the depression angle. Thus for frame 771 (slant range ~2.1 NM or 12,750 ft) and frame 783 (slant range ~1.8 NM or 10,930 ft), we have these illustrative pairs of terminal altitude values (Table 2) for different radar coverage depression angles, leading to various average descent slopes for the 36-second photo sequence.

Graphic from Shough analysis

Table 2. Radar depression angle and associated descent slope. Altitudes are in feet above terrain.

The actual practice approach slope is not known, but according to the Blue Book file the descent over the period of the UFO episode was from FL200 to about 9,000 ft MSL on a ground track of 24 NM, corresponding to an average of about 4.3 degrees. Considering the average slope of the entire approach, from FL200 at 38 NM to 1630 ft MSL at the runway, we find that this would be about 4.6 degrees. Since the final glide slope from the outer marker is known from the Minot AFB approach plates to be shallower than the 4.6 degree average, at less than 3 degrees, one would expect the average angle of descent prior to the final glide slope to be steeper than 4.6 degrees.

There is a deal of uncertainty in these values (we have an ambiguous value for the true range for departing FL200 for example), but crudely speaking they argue the likelihood of a descent slope somewhere near the middle of Table 2, about 2000 ft/min at around 5 degrees or so, corresponding to a radar depression angle (column 1) somewhat less than 50 degrees. This is not far from the bracketed bottom edge value (between -46 and -52 degs) deduced above from documentation, reassuring us that the basic construction is sound.

Taking 50 degrees as representative of the written specs, therefore, we have these altitude values for the initial and terminal frames of the photo sequence: 9767 ft above terrain (~ 11450 ft MSL) and 8370 ft above terrain (~10,000 ft MSL), reasonably close to the terminal value of about 9000 ft given by Col. Werlich in 1968.

ADDENDUM: Claude Poher has performed a similar but more detailed analysis to find a uniquely consistent model by covarying a number of parameters. The probable terminal altitude values found in Poher's work are quite close (within a few percent) to the values determined here using a different set of assumptions. This coincidence means that it is difficult to choose between the models on some indicators, but happily it also means that interpretations of the unidentified echoes (Section 6) are not very sensitive to uncertainties in the variables determining the model. (See for example: Claude Poher, “3.4. Refining the B-52 Position With Terrain Features;” and, "4.7. Discussion 1: The B-52 Altitude and the Tilt-up Angle of the Radar Antenna,” in Analysis of Radar and Air-Visual UFO Observations on 24 October 1968 at Minot Air Force Base, ND (2005)).

5-3. Summary and Conclusions on Time and Distance Data

As indicated above, attempts to reconstruct a totally self-consistent scenario have encountered problems, partly because of incomplete information but also because of anomalies in the information we have. These anomalies are principally: a) timing anomalies and lacunae in the RAPCON transcript; b) inconsistent accounts by Col. Werlich of the initial echo behaviour observed near the turn over the TACAN approach beacon at around FL200, >18,000 ft above terrain; and c) suggestions that the photo sequence belongs to the initial target behaviour observed near the turn. We will now attempt to use the result of Section 5.ii to help resolve some of these problems.

Firstly, c) is not only in conflict with Col. Werlich's contemporaneous reconstruction placing the photos at the end of the event, and with what natural practice would lead one to expect in the circumstances, it is also in conflict with the navigator Pat McCaslin's independent recall that he did not start the camera until the pilot suggested this some time much later in the event (see Note 4). Further, we have now shown that the altitude of the B-52 at the time of the photos is definitely inconsistent with the theory that the photos show the start of the event, but could indeed be consistent with Werlich's 1968 scenario placing them at the end. As will be shown below, the upper limiting target rates found from the scope photos are also inconsistent with the initial echo behaviour as described by Col. Werlich, although they could be consistent with the rate independently recalled by Clark.

For purposes of discussion it will sometimes be useful to divide the photos into two phases: Phase A, frames 771-3, interpretable as the rapid pass and transit of a UFO to a position off the left wing; then a lacuna in 774-5 where the echo (definitely in 774; arguably in 775) disappears; followed by Phase B, frames 776-782, the reappearance of the echo stationed persistently off the left wing, disappearing again in 783.

According to Werlich's early Memo for the Record, October 24 1968:

Initially the target traveled approximately 2 1/2 mile in 3 sec or at about 3,000 mi/hr. After passing from the right to the left of the plane it assumed a position off the left wing of the B-52. The blip stayed off the left wing for approximately 20 miles at which point it broke off.

Memo for the Record (0005-1)

There is certainly a similarity between this description and the Phase A sequence which shows echoes 1.62 miles off the right nose (#771), 1.05 miles just aft the right wing (# 772), then 1.05 miles off the left wing (#773). See Fig. 12. But Werlich's "about 3,000 mph" can't be recovered from this photo sequence (see below) and by the time of his October 29 telex Werlich has a different understanding of what the initial behaviour was:


Basic Reporting Data (TELEX 0008-6)

This time there is no mention of 3000 mph or of the target crossing from right to left of the aircraft. Instead we have only a "rapid" closure from 3 miles off the left wing to 1 mile off the left wing. Plainly the photos do not show a target 3 miles off the left wing at any time, neither do they show a closure from 3 miles to 1 mile as described here, so this description cannot be referring directly to them, even by mistake. But when we look at Werlich's map overlay of the UFO track in the Blue Book file (see Fig. 11 below) showing a closure of the echo from 3 miles to 1 mile off the left wing near the VOR beacon fix, it is equally clear that there is no 3000 mph closure here either: Assuming constant echo bearing from the B-52, the closure shown beginning at point b in the figure takes place on a track of about 3.5 miles over at least 8 radar scans (24 seconds or more), a ground speed of only about 520 knots. So this tells us that Werlich must have been referring to other information, about a different target movement, gleaned presumably from the navigator, Pat McCaslin, during the debriefing.

5-4. Initial Radar Events Near the Turn Over the TACAN Approach Fix

McCaslin's very clear recollection is that the target was first detected by him to the right of the aircraft on the outbound leg before the aircraft had completed its 30/180 turn back onto the approach heading. This sequence at first sight appears inconsistent with Col. Werlich's 1968 statement in the AFR 80-17 report telex that the echo appeared "after rolling out of [the] right turn". However, as we have seen Werlich's summary statements quoted above are themselves internally inconsistent and bespeak some confusion.

Werlich obviously realised quite soon that the photos which Clark had printed up were not taken (as Clark apparently had always believed they were) at the start of the incident, but rather at the end, and he makes this plain in the file. But it may be that this realisation was responsible, ironically, for the confusion that appears between Oct 24 and Oct 29 in his account of the start of event. He may have edited out his Oct 24 references to 3000 mph, and to the transit from right wing to left wing, because in his mind these features became conflated with the rather similar photo sequence originally, but (he now realised) mistakenly, placed at the beginning of the event. But although it may be correct that there had been confusion, Werlich's Oct 29 revision, rather than clarifying the issue, introduced further confusion.

It wasn't only Werlich. The evidence is consistent with a rather general confusion on this point, both in 1968 and since. As mentioned, it appears to have been present in Richard Clark's mind, and McCaslin's own recollection suggests that he may have conflated the photo interpretation and his own memory of the initial sighting in a very similar way.

McCaslin's account clearly describes fast motions of the echo only near the start, followed by its steady pacing of the B-52 off the left wing until the time it finally disappears. So when he describes (interview with Tom Tulien, Feb 2001) being shown the film sequence in a later debriefing at Minot, it appears that he is mistakenly associating these kinematics with the start of the event:

McCASLIN: . . . it’s that that they used to calculate the speed. That’s where I found out what the speed was, during that session. They said, ‘We figured the speed was…’, and I forget. It was a phenomenal amount of…it was a phenomenal speed. And what’s important about that is not the speed, but the fact that they could instantaneously go from one speed to the next, and then instantaneously resume the speed that the…the prior speed. That was more impressive to me than the actual speed, although that was impressive enough.

The same conflation occurs explicitly later in this interview. McCaslin had been sent poor copies of the scope photos in late 2000 and is describing how he interpreted them:

PM: The...the blip I saw would have been when we first picked it up.
INT: Okay.
PM: It was on the outbound leg. And...and the scope photos I saw had none from inbound. None.
INT: Oh, okay.
PM: All that’s missing.
INT: When you say ‘inbound’, at what...
PM: After we turned from the te-or after we turned and started our descent.
INT: Okay, you don’t see anything...
PM: All this stuff...all the stuff that I saw on that package was outbound.
INT: Okay. From the beginning of the incident?
PM: Could’ve been slightly prior.
INT: Oh, okay. Okay.
PM: But there...there was hard to tell because of the quality. I could tell from the heading that we were outbound. I could tell...I saw one blip, maybe two that were what I think is the...the return, and it was in the right position and all that stuff. Three miles out, off the right wing.

In fact, we now know that McCaslin was here misreading the photos. There are certainly none from the outbound leg at all. This is an understandable error because these were extremely poor prints made from microfilm copies of the Blue Book file; the investigators had not at this stage discovered the good quality set retained by Richard Clark.

graphic from shough analysis

Fig. 10. Image from Blue Book microfilm of frame #776. Just visible on this otherwise useless copy is the radial line at ~285 degrees caused by a 50 msec capping of the shutter to allow film advance.

The hypothesis is this: The radial feature that McCaslin is reading as the heading marker on the radar scope is actually a photographic artefact (Fig. 10). A thin line runs across the ground echo towards about 285 degrees due to the shutter closing briefly at the point of film advance between each 3-second scan (see discussion below). Because of the atrocious print quality the real heading marker was completely invisible. Bearing in mind that McCaslin had last looked at such an ASB-9 radar scope decades earlier, we can see how the illusion was naturally encouraged because the phony "heading marker" happens to lie close to the outbound heading on which he knew the B-52 was flying at the time the echo first appeared:

INT:   . . . . Those are probably the best copies we’ve got, right there.
PM:   Okay, see, you can’tell…it looks like…I can’t even tell the…hard to tell the time, even.
INT:   Yeah, I know. They’re hard to read.
PM:   Uh, but you can see…we’re outbound. There’s the heading indicator right there, the track.
INT:   Okay, that’s the direction you’re going…
PM:   And we’re headed northwest.
INT:   Are these the TACAN numbers?
PM:   No, those are the…that’s the…
INT:   Degrees?
PM:   …the heading. Yeah. So we were headed.
INT:   No, not even degrees, are they?
PM:   Yeah, they’re degrees. This is 280.
INT:   Oh, okay. I’m sorry. Okay.
PM:   So you’re headed northwest, right here. [ . . . ]
INT:   285.
PM:   285, yeah. We’re outbound.
INT:   Almost 290 [inaudible].
PM:   That could not be the inbound…
INT:   Okay.
PM:   …return. So this was…this was on the way out.

McCaslin's testimony appears unequivocal on the point that the radar event began before the turn with a strong echo 3 miles off the right wing. Indeed, when we look at Werlich's own map overlay in the file (see Fig. 11), plotting both the B-52 flight track and that of the unknown, we find that he indicates, in addition to the UFO track pacing the inbound plane off the left wing, another static location about 3 miles off the plane'sr ight wing on the inside of the outbound turn. This location off the right wing of the plane before the turn, and the location of the first appearance of the echo off the left wing after the turn, are both marked with the same red cross and are both connected to the B-52 flight track by what appear to be identical dashed lines evidently indicating lines of sight between synchronous positions.

Graphic from Shough analysis

Fig. 11. Diagram of B-52 and UFO tracks during the turn. The large open circle is believed to represent the VOR beacon fix for the approach pa at which the echo could have crossed from a to b in the space of 2 1/2 radar scans (7.5 seconds) at an average rate of about 3000 knots. (Approximately to scale. Adapted from Col. Werlich's map overlay).

McCaslin's first uncontaminated memory, as given to Jim Klotz in an interview in Nov 2000 without sight of other historical documents or witness statements, is worth quoting here:

PM: we were climbing out and approaching the VOR, I remember I noticed off to the right on the radar a faint return about three miles out, and uh… which would have made it to the north... and ah…
JK: .. OK, And you were headed west.
PM: .. We were headed west-northwest, I think, and then about uh…and then in the next sweep of the radar, it was a very bright return, and it was a big return, it was at least as big, maybe bigger than the return a KC-135 would make, which I’d seen many times.
JK: .. Wow.
PM: .. So I alert the pilots to that. I said ‘here’s an aircraft or something off the right wing three miles.’ Well, they could see nothing and they told me to keep them advised of it. As we approached the VOR, they were going to have to turn right toward this thing, so I told them, you know, ‘I’ll just keep an eye on it.’ And they turned right toward it and uh…and as it… as we turned right toward the VOR it moved off to the north and maintained that three mile separation, so as we rolled out, it was at three miles off our left wing, and we were headed back toward the base now, uh starting the approach. I alerted the pilots to that, and they still couldn’t see anything visually.

So this phase of the event appears to be corroborated directly by Werlich's 1968 map overlay and indirectly by Werlich's initial citation (Oct 24 memo) of details which we cannot trace to any other origin than McCaslin's testimony given in debriefing that day:

Initially the target traveled approximately 2½ miles in 3 sec or at about 3,000 mi/hr. After passing from the right to the left of the plane it assumed a position off the left wing of the B-52.

Memo for the Record (0005-1)

The simplest reading of this is that the transit from right to left of the aircraft was the initial 3000 mph motion. Is this feasible? Neither McCaslin nor Werlich describe this transit in detail so the significance of "2½ miles" is uncertain. But evidently 3 seconds is the crucial figure here, since this is the scan period of the radar, suggesting that 2.5 miles is just a calculated scan-to-scan displacement and does not have any other particular kinematic significance. Evidently the geometry of Fig. 11 tells us that a rapid target motion between Werlich's two " +" positions must, roughly speaking, entail some odd multiple of a half rotation of the radar if seen from some point coming around the top of the turn towards the TACAN fix, so 1½, 2½, 3½ etc. In fact, if we measure the distance between these positions in Fig. 11 we get about 6.3 miles, which at the cited rate of 0.83 miles/sec corresponds to a little more than 2½ rotations of the radar screen beginning at about the point marked by a small open circle in Fig. 11. This could conceivably be the origin of the vexed "about 3000 mph".

Alternatively McCaslin's own later description of this echo transit, as "maintaining a 3 mile distance", could be taken literally, in which case a much slower echo motion would have begun with the B-52 somewhere near the small black circle in Fig. 11. Then the origin of Werlich's "about 3000 mph" is back in contention. We could try to connect it with McCaslin's recollection that just after the transit the echo closed suddenly:

PM:   We started the approach, and uh, again it was out there at three miles off the left wing. At some point, I don’t remember what altitude, the pilots were descending toward the base, but at some point this thing, uh, from one sweep to the next it moved from three miles off our left wing to one mile off our left wing.

But even a displacement of 2 miles relative to the B-52 in 3 seconds is equal to a speed of only 2400 mph, not 3000 (correction for ground speed is negligible). There is also no indication of this specific movement on Col. Werlich's track overlay, nor any other unambiguous contemporary record of such a movement. So this issue cannot be definitely resolved.

5-5. The Radar Film Sequence

Howsoever, returning to the radar film sequence, the result of the present analysis suggests that Richard Clark was correct that the 13 photos which he ordered printed up were the start of the photo sequence, but that there has been some confusion, both in 1968 and since, between the start of the event (correctly recalled by McCaslin and ambiguously recorded by Col. Werlich) and the start of the photography.

Further evidence of this emerges when we try to explain why the first of the numbered frames, #771, appears to capture a half-revolution of the radar sweep, hitherto assumed to mark a change in the scan mode at the start of the event when the radar was first put into Station Keep (see Section 2 above). Training Manual CDC 3210K Vol.4 discloses that the operation of the camera, rather than being a snapshot of the PPI display capturing an image with a persistence comparable to the 3 second rotation time, is a time exposure, the shutter being open for virtually the whole 3 seconds. (I initially assumed that it was snapshot because the moving clock second hand and the number counter are "stopped" by a brief exposure. But the brevity is explained by the fact that the clock and counter are physically separate from the PPI and photographed through a different lens system. The images are combined by a double exposure.) The PPI exposure is controlled electrically by a loop from the antenna rotation mechanism. At a certain point the rotation closes a circuit and sends a voltage to the camera shutter and film advance mechanism, capping the shutter for 50 milliseconds during which time a motor winds the film to the next frame.

This momentary interruption appears to be marked by the narrow dark wedge visible on the photos between 280 and 290 degrees (strictly, capping the shutter for 50 milliseconds ought to interrupt the image over an arc of 6 degs; the wedge visible is always much less than this angle for uncertain reasons). This is the radial line suggested above as the origin of McCaslin's mistaken "WNW heading marker" on a negative print. Frame 771 therefore shows the shutter opening with the PPI sweep at about 100 degrees followed by a time exposure of approximately 1.5 seconds until a voltage from the antenna rotation mechanism trips the camera shutter, closing it at 284 degrees and causing a fresh frame, # 772, to be advanced into place. In other words #771 shows the instant, nearer the end of the event than the beginning, at which the camera switch was operated, rather than the instant at which the radar's Station Keep switch was operated.

The only evidence which on the face of it might contradict this scenario is Richard Clark's recollection that there were originally a great many more frames than the 13 he had printed, possibly over a hundred. A hundred frames would represent a further 5 minutes of photography, but the aircraft altitude is persuasive evidence that the photos we have were taken shortly before the echo disappeared, as stated by Col. Werlich in 1968, and Werlich's contemporary track chart shows a "radar film area" approximately 2.56 NM in length, consistent with 13 photo intervals of 3 seconds at the B-52 speed, not more than 13. A further 5 minutes of UFO photos after #783 seems impossible.

On the other hand, this is only evidence that there were no further frames showing anything of interest; it is not evidence that were no other frames. The B-52 did not land immediately, but executed a missed approach and went around at low level in order to overfly the reported "landing" location before finally putting down at Minot AFB. It would be natural practice if the radar was left in operation during this go-around, since one doesn't know that the target has gone for good, and indeed the aircrew testimony is that they were instructed by radio to film the ground during this overflight. Since the B-52 carried no operable camera other than the radarscope camera this can only mean that the radar remained operational and that the camera was running. Probably it was left running until touch-down or until the film ran off the spool so that the complete roll would have been taken from the aircraft after landing by the intelligence analysts.

This would be consistent both with Richard Clark's recollection that the camera was switched on belatedly (as concluded here) and left running until they landed, producing a great many frames, and with the fact that he said "I had them print every significant image", recalling "nothing of any value" on the later frames (see also Note 4). On the succeeding frames the altitude hole radius would dwindle rapidly, even with the antenna tilt at maximum elevation in Station Keep, and would vanish entirely long before the aircraft descended to a couple of hundred feet to execute its low approach over the Minot runway. After this the B-52 never recovered sufficient height for the altitude hole to reappear. They overflew the "landing" location at a reported 1500 ft, which is comparable to the minimum range of the display (the ~2000ft TR-hole radius caused by de-ionisation delay in the antenna duplexer). So these frames would not be able to show any targets in the air, only a scope completely saturated with ground return. It's very probable that the echo from any object on or near the ground would have been lost against the ground echo itself. But even if this ground-scan did contain latent information of use to someone who knew what they were looking for, Richard Clark did not not know about any UFO on the ground and was not himself asked to look for evidence of it.

graphic from shough analysis

Fig. 12. Diagram of relationship of PPI echoes in Phase A. Frames 771, 772 and 773 superimposed to indicate displacement of the frame of reference of the radar at 3-second intervals at the mean ~250 mph speed of the B-52. This is a simplification if the true renewal rate; see below. (Note: only approximately to scale. The range scale is slightly non-linear and changes between the first and subsequent rings). With all this in mind we can refer to the situation illustrated in Fig. 12 in order to begin to derive limits for the approximate true (average) target speeds that would be implied by the echo displacements in Phase A.

5-6. The Filmed Echo Speeds

Note first that if we use a constant 3 second update rate to calculate echo displacements relative to the B-52 and then correct for the ~1100 ft movement of the B-52 (average estimated groundspeed) per photo interval, we find maximum target groundspeeds in both cases (assuming co-altitude) in the region of 2000 mph. This appears inconsistent both with Werlich’s “3000 mph” and with Richard Clark’s recollection that the Bomb Wing intelligence photoanalysis in 1968 (presumably employing a similar correction with access to accurate air speed data) calculated a figure of approximately 3900 mph (presumably nautical miles per hour).

However things are more complicated because although the scan rate and the photo update interval are synchronised at approximately 3 seconds, the echo renewal rate also depends on the motion of the target. The renewal rate of a relatively stationary target or a target on a constant bearing will also be 3 seconds; that of a target with an azimuth rate will not, and the correction depends on the rate and on whether it is positive or negative in relation to the antenna rotation direction.

The trace rotation direction on the ASB-9 being clockwise it is easy to see that the total time interval corresponding to 460 degrees of rotation between the echoes captured on frames 771 and 772 is roughly (460/360) x 3 seconds, or 3.8 seconds, and the displacement (roughly 2.1 NM in 3.8 seconds relative to the B-52, assuming co-altitude) indicates a maximum velocity of ~ 1990 knots relative to the B-52. On the other hand whilst the blip on frame 772 follows that on 771 by more than one 360 degree rotation period, the blip on 773 follows that on 772 by less than one rotation. It must be painted when the trace has rotated only about 115 degrees after the triggering of the frame advance at the end of exposure 772 in order to appear on the screen at the time of frame 773. The trace has rotated about 160 degrees between the two paints. So, the displacement between frames 772 and 773 (approximately 2.1 miles in 1.3 second) indicates a co-altitude maximum of ~5870 knots relative to the B-52.

Neither of these speeds corresponds to anything in the original air force file. However, we should also consider that it is impossible to determine acceleration without a minimum of three points of measurement on any trajectory, so that each of these speeds is in fact only an average. When we take the overall average of these two speeds (which is equivalent to taking the average rate of a single accelerated target measured at three points, 771, 772 and 773) we get a co-altitude upper limit of almost exactly 3900 knots, suggesting that this is very likely the route by which a speed of "3900 mph" was arrived at by the Bomb Wing photoanalysts in 1968 as recalled by Richard Clark.

Of course this is a measure of displacement relative to the B-52. Applying small corrections for the approximate speed and heading of the aircraft then gives us true (average) ground speeds. This correction has the effect of somewhat reducing the true average rate of the first displacement and very slightly increasing that of the second, giving maximum coaltitude values of about 1873 knots (771-772) and about 5877 knots (772-773) with an overall average of 3875 knots (~ 4450 statute mph).

The reader will have noticed that the above displacements are measured assuming the default case of co-altitudinal targets (zero degrees relative elevation) and so are upper limiting values. I am grateful to Claude Poher for pointing out the importance of the unknown elevation angle(s) of the target(s). Because of the depression angle of the radar cover the physical distance between two target positions within the beam can be very much less than would be indicated by their slant ranges as projected on the PPI display. In other words this is a problem in spherical, not plane, trigonometry.

Graphic from Shough analysis

Table 3. Average implied groundspeeds. Showing dependancy on depression angle. Maximum values occur if the target is co-altitudinal with the B-52 (θ = 0°). Speeds are in knots.

Some limiting solutions, assuming horizontal trajectories, are summarised in Table 3. The -50 degree value represents the specification figures used in this analysis. Note that maximum speeds consistent with Claude Poher's reconstruction of the B-52 flight track, and a -45 degree coverage limit, would be slightly lower still. (The values for -60 degrees represent the coverage diagram in Fig. 3, although there is no good evidence that this diagram is other than schematic.) We can see that the range of possible implied groundspeeds is considerable.

6. Interpreting the Unidentified Echoes ››