LAKENHEATH-BENTWATERS

THE LAKENHEATH-BENTWATERS MESS

This is an attempt to unscramble the maze of accounts the page author has encountered concerning the August 13-14, 1956 RADAR-Visual UFO case at Bentwaters and Lakenheath air bases, in England. The following chart attempts to correlate the various accounts. Note that each sighting could have a different cause, and may be unrelated to any of the other sightings. The separate sightings are identified by [number]

The Sightings:

(L) The Evaluation:

Now that was a confusing jumble of accounts! Here is a list of observations the page author made, to try to reduce this down to something sensible:

(L) GENERAL SCIENTIFIC OBSERVATIONS:
1. We cannot assume that all of these sightings were of the same thing. Neither can we assume that they were all different objects.
2. We cannot assume that the ground observers saw the same objects the pilots saw, and we cannot assume that the RADAR picked up the same objects that were seen visually. Neither can we assume that they did not see the same objects.
3. Only four of these sightings [numbers 4, 8, 11, and 12] have sighting by more than one method of observation (ground RADAR, ground visual, plane RADAR, plane visual). Only two [4 and 11] are both RADAR and visual by any account other than McDonald's.
4. Note that the RADAR controllers were thinking in terms of missiles and planes from the Soviet Union or Communist Eastern Europe, not space aliens.
(L) UFOLOGICAL OBSERVATIONS:
1. Several of the known UFO-causing factors were at work:
  - UFO MODE - People were told there was an unidentified object in the area. Thus, every light and RADAR target unknown to a witness became the UFO.
  - TOLD WHERE TO LOOK - RADAR operators and visual observers were told where to look for the UFO, and they saw things there. Never mind that those targets and lights seen had nothing to do with the original report.
  - GORMAN EFFECT - A pilot dogfighting with a nearly stationary small object, especially at night, thinks the target is changing course and moving with amazing rapidity.
(L) RADAR OBSERVATIONS:
1. RADAR was relatively new then, and they were still learning about RADAR signal propagation. At that time, planes were routinely sent to the locations of unidentified targets, just to find out what kind of object or phenomenon was there. This was for the purpose of learning more about RADAR, not looking for invaders.
2. UFO sightings that appear only on RADAR are always dubious, because there are so many ways for the RADAR set to be fooled by conditions. Newer RADAR sets have devices that identify planes with transponders aboard, so RADAR UFOs are not as readily noticed by air traffic controllers now. In 1956, these devices were not in general use.
3. Misadjustment of the AGC (Automatic Gain Control) on the RADAR set can cause targets that are too weak to appear under normal conditions to become visible when no airplanes are within range of the RADAR set. They then just suddenly disappear when an airplane moves into range.
4. One possibility for the high-speed objects is abnormal ducting of signals from another RADAR thousands of miles away, operating on the same frequency, but using a different antenna rotation rate.
5. Another good possibility for the high-speed objects is a third-trip or fourth-trip echo of the Perseid meteors. The date is correct for observation of this well-known meteor shower. A third-trip echo slows the meteor speed to 4000 mi/hr, and also reduces the altitude. Note that only one RADAR set picked up the high speed objects. Perseid meteors could explain some of the high-speed lights too.
6. The sweep rate of the RADAR became a factor here:
  - Nobody seems to have noticed that, while the object was seen for only 3 or 4 sweeps, it crossed the center of the RADAR. So the time duration should have been 1.5, 2.5, or 3.5 times the sweep rate, not an integer multiple of the sweep rate. But the calculations of time may have been erroneously made using integer multiples of the sweep time.
  - The 12000 mi/hr object was said to transit 55 miles in 2.5 sweeps time, taking 16 seconds to do so. That's 22 miles per sweep. How were they sure that the blips were caused by the same object, being 22 miles apart? Notice that this object was seen for only 4 sweeps.
  - That 2.5 complete sweeps occurred in 16 seconds indicates that one sweep on the Bentwaters RADAR takes 6.4 seconds. This set is an MPN-11A with an MTI (Moving Target Indicator) retrofit with AGC (Automatic Gain Control). It is now known that the operator can change the sweep rate with a variable speed control.
  - The Lakenheath CPS-5 is an ASR (Airport Surveillance RADAR) with an MTI & AGC retrofit. It probably has a 15 second sweep period.
  - How can anyone see a "swift circling motion" on a CPS-5? To see that it was a circling would require at least four blips. Most ASRs use 15-second sweeps, as does this one. At 15 seconds per sweep, the time-span of this "swift circling" would be 45 seconds. It is more likely that the RADAR men assumed a circling, because they were looking for aircraft characteristics.
7. The path objects took on the CPN-4 RADAR used by Ground Control is not documented. The person making the report said he had to call (presumably by radio or phone) the operators of the CPN-4, so they must have been remote to his location.
8. Likewise, how did the controllers know which target was the Venom and which was the UFO? Transponders were not used with that set, so there were no identification marks on the screen. With 15-second sweeps and close positions, they could have easily mixed up the two blips, provided they were not distinguishable by strength or size. Did they assume the one "behind" was the UFO? Was this because the pilot could see nothing, either on RADAR or visually? The Venom had no tail RADAR, and most accounts say the pilots had no visual sightings of this object.
9. Only by comparing the location of a target with its location one sweep ago can a RADAR operator determine the direction of travel. It is impossible to find the instantaneous heading of a rapidly maneuvering object with the equipment they had then.
10. It is very possible that the UFOs were randomly moving weather modifications of ground returns that happened to roughly coincide with the Venom's movements. It is also possible that a moving corner reflector, such as a dump truck or rail gondola car, caused a secondary image of the Venom. This would not explain the stopping of the UFO south of Lakenheath, unless an unrelated target appeared there at the time.
11. After sighting [4], the crews at Lakenheath and Bentwaters went into what the page author calls "UFO mode." This means that they were actively looking for unidentified targets. From this point on, all of the normally occurring spurious targets, and any lights seen in the sky, became UFOs. They also switched their RADARs to MTI mode, causing the changing edges of any anomalous, spurious, or weather targets to be amplified to look like plane echoes.
12. Only McDonald states that more than one ground RADAR location picked up the same object. All other accounts state that the last Bentwaters sighting was over an hour before the first Lakenheath sighting.
13. MTI (Moving target indicator) was extremely buggy back then. Remember that they were still using vacuum tubes and mercury delay lines back in 1956. It basically made all changes in the RADAR picture appear as blips. It made spurious or weak weather and anomalous propagation echoes into blips stronger than planes make, because the echo is constantly changing position and strength. It also made all real targets appear the same strength.
14. One of the first MTI installations was made at Washington National Airport just before the RADAR sightings of July 19-20 and July 26-27, 1952. That sighting was caused by the same MTI error. But it also included the automatic gain misadjustment, because the UFOs disappeared from the RADAR screens whenever a real airplane entered the tracking area.
15. It is interesting that one of the RADAR operators at Lakenheath, Sgt Perkins was also an operator in the Kincheloe AFB Michigan case on September 11-12, 1967, where the same type of RADAR UFO was detected. That case was identified as moving anomalous propagation.
16. In all three cases (Lakenheath-Bentwaters, Washington National, and Kincheloe AFB) the MTI had just been added to the RADAR sets. Could operator unfamiliarity have caused the MTI and AGC to amplify weak weather and anomalous-propagation targets to plane-blip strength?
17. MTI also made it harder to tell multiple reflections from true targets, because they were all amplified and clipped to the same brightness.
18. A stationary target shown on MTI is one of the following:
  - A RADAR set malfunction.
  - A misadjustment of the MTI gating level, automatic gain, or delay line timing.
  - A standing wave in the mercury delay line in use in 1956.
  - Ducted interference from a distant RADAR, normally too far away to detect.
  - A weak target with changing intensity. It fools the MTI into thinking it appears and disappears too fast for the eye to see. Weather can do this. This type of target can seem to be stronger than a real airplane, because the signal is intermittent and is not partly removed by the MTI.
  - Anomalous propagation causing the RADAR beam to strike the ground at slightly differing ranges for each set of pulses. This can seem stronger than a real airplane for the same reason as the previous case.
  - A tightly circling or spinning object, such as a bird tagged with a metal clip.
  - The spinning rotor blades of a hovering helicopter.
  - A slowly moving, but oscillating object, such as a steamboat rolling in waves.
  - It will not be a true stationary airborne or ground target. The MTI will correctly remove those.
19. Neither Sculthorpe nor London Airport picked up anything in their overlapping coverage areas. This is the strongest indication that that no real solid objects were present at the indicated locations. Neither of these installations had MTI.
20. Second-trip echoes (and multiple-trip echoes) are a possibility for some of the RADAR sightings. In this, the RADAR picks up a return from a target after another set (or several sets) of pulses have left the antenna. This causes the speed and distance to appear to be much smaller than they really are:
  - Multiple-trip echoes of the same object appear in different places and follow different courses on RADARs sited at different locations.
  - Multiple-trip echoes of the same object appear at different ranges on RADARs using different pulse rates, but sited at the same location.
  - A meteor can appear as a slower object moving within the lower atmosphere, due to multiple-trip echoes (the echo is several pulses late).
  - MTI and AGC will enhance and amplify weak multiple-trip echoes, making them much more noticeable.
  - Why they call this a "second-trip echo" is unclear. It should be called a second-pulse echo, because it returns after the second pulse is sent out.
  - In the early 1960s, they had to reprogram BMEWS (Ballistic Missile Early Warning System - a very sensitive RADAR system) to ignore multiple-trip echoes from the moon. That's a 2.5-second round trip, or many pulses later!
21. Secondary reflections from corner reflectors on the ground (dump trucks or gondola rail hopper cars) can cause two images of an airplane to appear on RADAR. The controllers might have thought the second image was the UFO.
(L) VISUAL OBSERVATIONS:
1. No visual sighter can estimate the altitude or speed of an unknown light in the night sky. It's impossible to do!
2. The timings of the visual observations are not accurately determined. Some of them could be meteors.
3. It is not known if the Venom pilot in chase number 2 was running from a visual object, or an object the RADAR controllers were saying was behind him. He seemed quite scared, from what he said to the other pilot, but was that due to being chased by a light, or being followed by an invisible object on RADAR (as told to him by the controllers)?
4. Nobody took data on the angular motion of the visual objects, just the guesses of altitude and speed made by the observers.
(L) OBSERVATIONS ON SIGHTING NUMBER [4]:
1. Sighting [4] is the only remaining unidentified object.
2. It might have been a small missile, accidentally launched from a ship, and covered up by the military. This is weakened by the fact that no other RADARs picked it up.
3. One possibility is an (illegal) amateur rocket. But the probability that it coincidentally went in the same direction as the RADAR targets before it is quite low. And it also was not picked up by the other RADAR sets. This might not be a problem if it was made mostly of nonmetallic materials.
4. It also could have been a meteor. This works only if the pilot saw a reflection of it in the sea or a swamp, or he saw something else at the same time. The RADAR sighting would be a multiple-trip echo.
5. Another possibility is that the pilot, alerted to unidentified objects in the area, passed close to a lighted weather balloon, and reported that as a high speed object.
6. It could be a coincidence where three different objects, each detected by one set of observers, chanced to overlap in time.

(L) Notes about RADAR:

Here is a look at what really happens in a RADAR set of 1956 vintage. The sequence of events given is for one single pulse sent out by the transmitter:

The blanking circuit locks off the electron beam in the display tube, and the receiver input is muted to prevent damage during transmitter operation.
The sweep circuits return the electron beam position to the center of the display tube.
The transmitter sends out the pulse. It moves away from the RADAR antenna at the speed of light (186000 mi/s or 300000 km/s).
The sweep circuits start moving the electron beam away from the center of the display in the direction the antenna is pointing.
The receiver is enabled, and the blanking circuits enable the electron beam.
As the sweep moves away from the center, the weak electron beam leaves the visible line that is seen to be slowly rotating around the tube as the antenna rotates.
The transmitted pulse strikes a target (if present), and part of it is reflected back to the antenna. The time it takes for the pulse to make the round trip determines the distance from the RADAR set.
The receiver picks up and amplifies any returning echo (if present).
If the MTI is on, the echo is amplified further and clipped, then fed to a gating circuit that decides whether or not an echo is there.
The resulting signal is fed to the display driver. If the MTI is on, the signal is also fed to the mercury delay line. The delay line is adjusted to delay any signal fed into it for exactly the time between transmitter pulses.
The display driver strengthens the electron beam in the display tube whenever it receives an echo signal. If the MTI is on, a delayed echo from the previous pulse will shut off the electron beam for an instant, canceling out any echoes received at the same location as the delayed echo.
The strengthened electron beam makes a much brighter spot on the display tube. The brighter spot persists much longer on the slow-decay phosphor coating than the weak sweep line does. It will usually persist for several rotations of the antenna before the phosphor loses all of its energy.
Any further echoes received by the antenna are handled in the same way as the electron beam continues to move out toward the edge of the display tube.
During all of this, the antenna and the sweep coil have rotated a very small fraction of a degree.
When the beam reaches the edge of the tube, the whole process repeats. Any echoes from the pulse just transmitted that are received after this point are treated as though they came from the next pulse. These are called second-trip echoes. Those received after several pulses have been sent are called multiple-trip echoes.

Thus, the RADAR set determines the location of an object by using two values: The direction the antenna was pointing when the echo was received, and the time since the last pulse was transmitted. Of course, extraneous signals, such as those abnormally ducted from distant RADARs, second-trip and multiple-trip echoes, multiply reflected echoes, and electronic noise can also be displayed just as though they were valid echoes. The MTI clipping and gating makes these spurious signals seem as strong as real echoes from planes. A misadjusted AGC can amplify these effects.

(L) Conclusions:

Here are the conclusions drawn from the above evaluations:

The initial high-speed sightings were probably Perseid meteors. The date corresponds with the maximum meteor frequency.

Most of the RADAR sightings were anomalous propagation, amplified by the MTI and AGC circuitry.

One important thing to note: The RADAR sightings at Bentwaters were quite different from the ones at Lakenheath.

Most of the visual sightings were single lights. Many of them could be airplane lights, including the planes sent to look for the UFOs.

The RADAR sets were recently retrofitted with MTI and AGC.

The whole case seems to be the result of unfamiliarity with the newly installed MTI and AGC, failing to correlate with other stations, failure to take good data at the time of the sighting, panic caused by the thought of UFOs (or Soviets), and a compounding of unrelated events occurring on the same night into one case.