People Sniffers

In July 1969, 3 Troop were overflown by a US aircraft fitted with a 'people sniffer'.

I understand that this is a device which senses the ammonia in sweat and urine (also fitted to 9 Sqn and 161 helos). Some animals were undoubtedly a bit unlucky, as were 3 Troop who were subsequently targeted by a US 155mm battery. There are obvioius lessons here about co-ordination between Allies in terms of maintaining accurate records of troop positions etc.

My question to anyone who might be able to help is: why weren't heat sensors more effective? Was it that heat didn't rise above above the canopy, whereas ammonia did?

Appreciate advice...sometimes research data raises more questions than it answers.

Many thanks, Bruce

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From reading about the surveillance done of the HCM trail...I think the answer is that IR detectors could have been employed in areas like Phuoc Tuy, however, the sensitivity of the dectectors was such that, while they picked up trucks etc, they wouldn't have detected body heat (or even cooking fires). Far better, therefore, when no engines were involved, to use detectors which picked up minute traces of ammonia.

That's my theory to date anyway.

Bruce

Bruce, Would someone from 161 Recee be able to assist or point in the right direction?

TH

Hi Trevor,

There's a good account of the use of people sniffers in the 161 book 'Possums and Bird Dogs'. So I'm pretty well up on that, but the IR detector story is another matter.

With the technology we're familiar with now, it's easy to think of a US survellance aircraft picking up the heat from tank engines and passing the info to an arty battery. It's frustrating because it's so easy to assume such things. In 1969, it was a different situation and IR surveillance was concentrated on the HCM trail.

Fortunately for the tank troop involved, they weren't picked up by the US helicopter teams which involved one helo using a starlight scope working with another using an IR searchlight. If something was picked up, the IR was turned to white light and the target engaged. I'm pretty sure that the tank troop were detected with a people sniffer.

Bruce

Hi Bruce,
Not sure this answers your question, but here goes on 3 troop's experience in Bien Hoa province.

The U.S. 'intelligence' was remarkable re the grid references we would be given in code, to be followed by us jungle bashing, sometimes for days where we always would find a bunker system that had been decamped within hours, or recently abandoned. We are talking anbout a number upward of at least 8 - 10. Alex Smith would know.

As in the instance of the 155s, most nights when we were in the bush, a 'plane', think it was a jet of some description, but cannot be sure as never actually sighted it - would overfly somewhere within our vision, but seldom overhead, and every so many seconds there would be a flash of white light.

What and how it was operating for detection, have no idea. It definietly flew over us earlier on the night of the 155 episode.

Regards John Wedmaier.

Guys, have been thinking while I fed horses.

What about the enemy, re these 'sniffers'. With the information the Americans had gleaned re our position, they were on to us with three ranging shots.

Also I've realised there is no blame to oportion either re this incident...it was not a predetermined stop, so we would not have notified a grid reference to anybody. We had to allow time to set up the leagure before dark, and for the guys in the track to make scrapes. (Poor bastards, they were more like scratches than scrapes. Wow, did they dig.)

While remembering an American freaquency that we had come off only a day or two before gave us breathing space; I have since realised that a crucial element was that we knew the progression of laying on a target so well...only we were the target. When we heard the round that went directly over us ....s were trumps.

Aa an indication of my/our fear, like others, I had been remiss on basic maintenance and could not close my hatches, ripping off fingernails in the attempt.

As to the terror of that night, with full respect realising that many others were involved in heavy contacts during their time, I was showing my grandsons the tank that is at Hilly's place. When I went to close down the tank after the inspection (the kids loved it), the operator's side would not close. While leaning in from the outside trying to move the latch I broke out into a massive sweat.

Thank you to all the above and those who have contacted me separately.

I'm now aware of the Mohawk OV-1C in particular and the use of its IR photo flash cartridges to produce near real-time results and ability to communicate these to artillery batteries. There was another system which involved a strobe light...but how any of them work is beyond me.

Suffice to say that the "flash" referred to by JW could well have been from a Mohawk above.

Bruce