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On the Guestbook page of this web site, an individual signing the name "Paul Rifenberg" left the following message (July 4, 2000):


Okay, Colonel. . .I have a question for you. During the Senate Select Committee hearings, testimony was given that spike sensor pods were air-dropped along the Ho Chi Minh Trail. Their primary function was to be used as motion detectors, to sense troop and equipment movements. However, they could also be used by American pilots who had been shot down to manually enter their pilot authenticator codes while they were evading capture, or even during an escape attempt. The testimony reported that no fewer than 20 (twenty) such manual entries were made. Could you enlighten us as to how many of those "cries for help" were made SINCE the end of hostilities, and how many of those pilots were actually recovered ? If your answer is that that is classified information, why hasn't it been de-classified now ? Just curious. . .I am sure others are too.


I sent an e-mail message to Mr. Rifenberg asking him to cite for me the name of the individual making this claim and to provide me with a copy of the testimony in question.   As is usual with the MIA activists when challenged to provide facts, Mr. Rifenberg responded with a bit of fancy footwork.  Here is his answer to me:

QUOTE (E-mail from RifenbergP@aol.com, 7/5/00, 8:25PM)

Colonel Schlatter,

I didn't ask you to believe or disbelieve anything.  I simply posed a
question.  I wasn't the one who testified to the sensor pods.  In fact, the
individual who brought the subject up during the hearings was making an inquiry
then, just as I am now.  In both instances, no one admitted to to anything.

If it is your position that no downed pilot, at any time, ever manually
entered his pilot authenticator code into one of those sensors, then that is
your official answer.  Why don't you print your response on your message
board, so others can be similarly enlightened ?


Well, the give you the short answer, yes, Mr. Rifenberg, it is my position that no downed pilot -- or anyone else for that matter -- entered his "authenticator code" into a "sensor pod."  Now, let's get on to the long answer.

(Let's insert here that I spent a couple of hours searching the final report of the Senate Select Committee -- I found no mention of such statments, testimony, or claims as referred to by Mr. Rifenberg.)

The Sensor War


The Vietnam War saw the introduction of a lot of technology to the battlefield -- some of it worked, some did not.  One type of technology that worked and that would later be developed into far more advanced devices was that of unattended sensors.   Basically, the problem was how to monitor areas or points for enemy activity.   Ideally, US recon teams would watch trails, base camps, and the like for enemy activity. However, given the remote nature of the jungles of Indochina, the finite number of troops available for use in recon, and the fact that putting troops out into enemy-controlled territory often proved fatal to troops, perhaps there is a better way to monitor areas for enemy activity.

Department of Defense researchers had for years used remote sensing devices to monitor areas of interest.  The most common use of remote sensors is sonobuoys. Picture a buoy floating in the ocean with a sensitive directional microphone coupled to a radio transmitter, all powered by a water-activated battery.  The buoy transmits to a monitoring station every sound that it hears.  Trained specialists listening to these sounds can tell the difference between a pod of whales and a Russian submarine.  Now, this is a very simplistic description of the sonobuoy but that's about the size of it.   The US has for years maintained a network of sophisticated listening devices on the ocean surface and ocean floor to track Soviet submarines.  For a good account of this activity, read the book Blind Man's Bluff:   The Untold Story of American Submarine Espionage, by Sherry Sontag.

Why not use the same principle to monitor activity in areas on land where we do not want to risk putting men, or to provide 24-hour monitoring of areas where we occasionally insert men?  Why not indeed.

Sensors in Vietnam

I served three years in the field artillery, including a tour of duty in Vietnam as an artilleryman.  I then transferred to Army intelligence where, in one of my assignments, I was part of a team that evaluated one aspect of the use of unattended ground sensors in Vietnam. During that project, I gained some understanding of the sensor war in Vietnam.

In Indochina, US forces employed several types of unattended ground sensors.  The idea was to:

  1. build a sensing device that would detect movement, sound, or even infra-red emissions (heat from vehicle engines);
  2. camouflage that device so it looked like a normal piece of vegetation;
  3. deposit the device into an area of known or suspected enemy activity;
  4. monitor the device for activation;
  5. take some sort of action when the sensor was activated.

Types of Sensors

There were several types of unattended ground sensors deployed in Indochina.   Sensors could be divided into categories depending on sensing method and construction.

Sensing methods
bulletSeismic.  These sensors contained seismic detectors.  That is, they detected movement in the earth -- similar to earthquake detectors -- such as vehicle(s) moving past or footsteps.  Seismic devices required a small spike to be driven into the ground; this spike contained the sensing element.  If the ground moved, the sensing element moved and activated a radio transmitter that transmitted a beep, alerting the monitor to the fact that something was moving near the sensor location.
bulletAcoustic.  Acoustic sensors are similar to sonobuoys -- they contain one or more sensitive microphones attached to a transmitter and they transmit whatever sounds they pick up.
bulletInfra-red.  These sensors are sensitive to changes in ambient temperature.  If a warm body -- human, truck engine, water buffalo, tiger -- came close to the sensor, it sensed the rise in air temperature and caused an internal radio transmitter to transmit a beep.

Sensors came in various sizes and shapes.

bulletSensor pods.  These devices were fairly large.  As I recall, they were 6 to 8 inches in diameter, 3 to 4 feet long, and contained one or more microphones or other sensing device, a radio transmitter, a battery, and an antenna. 
bulletThe device was in a metal canister, painted with camouflage paint.  The antenna was built to look like a small sapling or jungle plant. 
bulletPods contained acoustic sensors (microphones) and seismic sensors.  Useable life was battery life.
bulletThe canister had a pointed end, was dropped from an airplane, and would (hopefully) bury itself in the ground, leaving the microphone exposed and burying the seismic detector.   The transmitter would transmit any sounds or ground vibrations that it picked up to aircraft or other monitoring station.
bulletThe idea was to drop several of these along a road or trail -- hoping that the dropping aircraft could get them delivered -- then monitor their output.  When sounds such as truck engines were heard or when heavy seismic activity was detected, then artillery or air strikes could be called in on the area.
bulletScatterable sensors. 
bulletThese were small devices, mostly seismic. 
bulletThey consisted of a seismic detector, a transmitter, and internal antenna, and a battery in a fiberglass or plastic case made to look like a broken branch, a big leaf, or other piece of forest litter. One type of sensor was designed to look like -- I am not kidding -- animal droppings.  (Most of these things were Seismic Intrusion Detectors -- SIDs.  These latter types were immediately named "TURDSID" by the guys using them.)
bulletThey were usually delivered by air, just dump a batch of them out along a trail, road, or in a suspected base camp area.
bulletBecause they were small, their batteries were small and transmitters were small.   Battery life was not long -- a few days.
bulletManned sensors.
bulletAs an artillery forward observer, I operated with infantry units.  One unit had some test sensors that were used in perimeter security.  The sensor consisted of a small box containing a battery, transmitter, and antenna.  Attached to it were several (four, I believe) long wires, each with a seismic stake on the end.  The stake was about the size of a tent peg.  There was also a receiver, tuned to the frequency of the transmitter.  The idea was that the sensor box would be put, say, along a trail leading to an ambush site and the spikes pushed into the ground.  Each spike transmitted a different beep.  When something came down the trail, it would activate the seismic sensors, a distinctive beep would be transmitted to the receiver, and people in the ambush would know where the movement was.
bulletHere's a photo of one type of sensor

adsid.jpg (6941 bytes)

This is an "ADSID" -- Air Delivered Seismic Intrusion Detector -- it detected movement in the ground and broadcast a signal to a monitoring station, either airborne or ground-based, alerting the monitors to movement.  This device is 31 inches long and weighs approximately 26 pounds.  Battery life was from two to 45 days, depending on mode of operation settings.

Sensor employment

The principal employment of sensors was along roads and trails used by North Vietnamese forces.  A lot of sensors were dumped along the "Ho Chi Minh Trial" in Laos.  Remember, the Ho Chi Minh Trial was NOT a big, single superhighway along which moved PAVN supplies and troops.  Instead, the Trail was a network of jungle roads, trails, footpaths, bicycle paths, and the like.  If we bombed out a section, PAVN either rebuilt it or moved to the other side of the river or mountain.  Because Mr. Rifenberg has claimed that downed US aircrews entered their "authenticator codes" into these sensors, let's focus on employment of sensors along the Trail.

The vast majority of sensors deployed along the Trail were airdropped.  That is, an aircraft -- usually a high-performance aircraft such as an F-4 or F-105 -- flew along a known or suspected portion of the trail and dropped out one or more sensors, thereby seeding the area with sensing devices.  Other aircraft -- usually aircraft on electronic surveillance missions -- would listen in on the frequencies of the sensors and report any activations.

Excellent website dealing with the sensor operations

Check out this page:  http://home.att.net/~c.jeppeson/igloo_white.html

The idea does not work

Mr. Rifenberg would have use believe that these sensor pods had some sort of device whereby a downed US aviator could walk up to the sensor, open a trap door, and punch in a code.  Sort of like making a telephone call saying "Come get me."   This is absolute rubbish.  Consider a few facts.

  1. How is the downed US airman to know where the sensor is located?  These things were dropped from fast-moving aircraft and their location was in a general area, not a specific, known point on the ground.  Please don't try to tell me that every aircrew member carried with him the latest listing of grid coordinates of sensor pods -- it's just not that precise.
  2. How is the US airman to know how to find the sensor? If you are going to find something -- in the jungle, in a city, in your own home -- you must first know two pieces of information:  exactly where you are and exactly where the item you are seeking is located.  Knowing where you are, and knowing where your target is, you then know which direction and how far to travel.   Would someone please tell me how a downed airman knows exactly where he is and exactly where a sensor would be located?  Remember, we are talking here about the 1960's and early 1970's -- long before the advent of the GPS satellites and receivers.  Downed aircrews knew what country they were in and generally where they thought they were -- no one knew his position with any precision, certainly not with sufficient precision to find a tiny device hidden and camouflaged in the jungle -- and he did not know the location of the device to start with.
  3. Why go looking for trouble? Remember, sensors were dropped in areas of known or suspected enemy activity.  Why in the world would a downed aircrew go walking into an area of known or suspected enemy activity in search of something that he is not going to locate?  Downed aircrews were doing their best to avoid enemy activity, not walk into it.
  4. Finally, sensors did not have such a capability.

So, to answer Mr. Rifenberg: 

The idea that downed US aircrews -- or any other US personnel lost in enemy controlled territory -- located an unattended sensor and made a long-distance phone call for help is ludicrous.  I don't doubt that someone somewhere has claimed that he knows that such happened and that he personally monitored these calls for help.  Never happened.

Update (October 29, 2000)

Daly's claims

The plot has now become thicker.  In early October, Mr. Rich Daly, another MIA "activist" -- from Minnesota -- came up on the newsgroup alt.war.pow-mia.   Daly tells the following tale:

bulletIn a Congressional hearing -- not further identified -- Delores Alfond (founder and director of the National Alliance for POW-MIA Families, a regular source of bogus stories) stated that she had a report, or that she had heard -- Daly was not certain which -- about "pilot authenticator codes" from missing US personnel having been broadcast by unattended ground sensors in SEAsia as late at the mid-1970s.
bulletAccording to Daly, Senator McCain stated that he had "seen a report about this" but that it was classified.
bulletDaly stated that such a report had not been located and that "DIA" had denied that any such report existed.  This fact -- if it is a fact -- in Daly's mind proves that it happened and that there is a cover-up in progress.

Now, Daly is convinced that US personnel, lost in SEAsia, were locating these sensors in the mid-1970s, entering their "authenticator codes" into the sensors, and waiting for rescue.  Daly's posts to alt.war.pow-mia generated a lot of responses from folks trying to tell him that such claims are total nonsense.  Anyone who is interested is welcome to go to deja.com and search for alt.war.pow-mia or for Rich Daly.

In one of his newsgroup articles, Daly mentions having interviewed former US Army Major Mark Smith for "six hours" and that Smith told him about the sensor activations in the mid-1970's.  Now there's a reliable source for you.

It is also interesting to note that the original question to me regarding "pilot authenticator codes" and sensors came from Paul Rifenberg, who, when I asked for details replied, in part: "In fact, the individual who brought the subject up during the hearings was making an inquiry
then, just as I am now.  In both instances, no one admitted to to anything."  
Rifenberg says ". . . no one admitted to anything."  Daly says that McCain said that he had seen a report.  These clowns really need to talk to each other and get their stories straight.

If -- and this is a big "if"   -- McCain said anything about sensors, I doubt he said he had seen such a report.   In fact, he could not have seen a report about "pilot authenticator codes" being heard over sensors because such a thing never happened.  McCain may have commented about having seen a report on sensor operations in Vietnam.  I suspect that, if McCain said anything at all, it was a case of "what the Senator meant to say was . . . "


The sensor program had nothing to do with the search for missing US personnel; the devices were not capable of having an individual enter his "authenticator code" or any other information into the sensor; and, no one lost in the jungle could find one of these things anyway.  Not to mention that battery life was from 2 to 45 days.  Not likely that in the mid-1970's anyone was sending signals from sensors that had been dropped years previous.  None of this, however, will deter Daly, Rifenberg, Alfond, or other true believers.

Posted July 5, 2000.